A week and a half after his return, he went to the 15th floor of the Continental Life Building in downtown Fort Worth. Earlier that morning, my father, a successful petroleum engineer, received a call from a young man who wanted certification of fluency in Russian. Rather than tell him that there wasn’t much of a market for a Russian translator in 1960s Texas, my father, who fled Siberia during the civil war, welcomed the chance to meet this fellow Russian speaker in person. He told him to come in for a meeting.

Around 11 a.m., with the temperature climbing into the 90s, a slight, 22-year-old Oswald arrived, drenched with sweat and wearing a wool suit. My father asked Oswald to translate passages from a Russian book he chose at random, and he was surprised at how well the young man performed. He asked his secretary to type out a “to whom it may concern” letter stating that one Lee Harvey Oswald was qualified to work as a translator, but he also told him that he knew of no jobs in the area that required knowledge of Russian. To soften the blow, he invited Oswald to lunch at the Hotel Texas, a block from his office, with its bustling dining room filled with deal-making oilmen, bankers and lawyers gnawing on Melba toast, a specialty. As they ordered their lunch, my father tried to engage Oswald about his wife and life in contemporary Russia, but the young man volunteered little about how a former Marine and Fort Worth resident could end up in Minsk other than to say enigmatically that he had “gone to the Soviet Union on my own.” Upon parting, Oswald offered the address and telephone number of his brother Robert, with whom he and his wife were staying, just in case anything came up.

Nothing did, of course, but there were so few émigrés in the area that the Dallas Russians, as my family called a group of their friends, felt protective of their own. A few days later, my father decided to check up on Oswald and his wife, and because I was around their age and home for the summer, he took me along. When we pulled up to the house on Davenport Street, we were greeted warmly by Robert Oswald, a tall and well-spoken man, who had served in the Marines and was working his way up to management at Acme Brick Company. Lee, by contrast, was restrained. He was short and wiry, his hairline noticeably receding, and he spoke with a Southern accent, not Texan, perhaps a relic of time spent in New Orleans during his youth.

Lee and Robert invited us in to meet Marina, who was slender, almost fragile, with a natural beauty. (Lee was one of several suitors back in Minsk.) She smiled rarely, if at all — a typical victim of Soviet dentistry, she was ashamed of her teeth. Lee explained to his wife in Russian that he had invited over a pair of fellow Russian speakers as a favor. And so my father, Pete, led the discussion by asking her questions about their voyage to the U.S., life in Minsk and what it was like to be a young person in the Soviet Union. Marina answered most of the questions, speaking quietly and occasionally showing photographs.

About a week later, my father and I drove 10 minutes from our house to Lee and Marina Oswald’s new home, a cramped one-bedroom duplex near the Montgomery Ward building. Their yard had a hardscrabble lawn burned yellow by the Texas summer sun, and the front door stood on a little porch, up a single concrete step. My father was taken by Marina. She was an engaging young woman who had already overcome a great deal — she was reared in a war-ravaged St. Petersburg (then Leningrad) littered with unmarked graves — and he wanted to help her. He asked Marina if she would offer me Russian lessons. Before we even set a fee, Marina agreed to see me twice a week. She seemed happy for the company..

The next Tuesday, at around 6 p.m., Marina invited me in for my first lesson. The Oswald living room was extraordinarily bare; there was a shabby sofa and chair and a worn coffee table where a copy of Time magazine featuring John F. Kennedy as its Man of the Year was prominently displayed. (The issue, which would curiously remain in the same place during all my visits, was dated Jan. 5, five months before the Oswalds’ arrival in the U.S.) We sat there uncomfortably for some 20 to 30 minutes until Lee burst in the door, dressed in his customary simple slacks, a plaid shirt with open collar and sleeves rolled up to the elbows, carrying a stack of weighty books from the Fort Worth public library. The conversation segued to the Time cover; Marina ventured that the president appeared to be a nice man and that the first lady, at least from the pictures she had seen, appeared quite glamorous. She also said that she seemed to be a good mother. Lee, in his curt way, agreed.

As our first session came to an end, we decided that future lessons would take the form of my driving the Oswalds around town and having Marina correct my practical Russian as I pointed out landmarks. This, we reasoned, would be better for my language skills and help Marina learn the city. But we all knew it would also greatly benefit their ability to run errands. At the time, I thought that Lee, who did not have a driver’s license, seemed to recognize that I was doing his young family a favor. As I was leaving their house, he raced to the bedroom and returned with a faded pocket English-Russian dictionary that he used during his time in Minsk. “Take this,” Lee told me. Only later did I realize that Oswald was showing off in front of Marina, pointing out that he didn’t need the dictionary but that I did.

On a typical lesson evening, I would show up around 6:30, when Lee got home from his welder’s job. We would climb into my yellow Buick and drive by department stores or Montgomery Ward, and I’d bring them back home by 10. These were lean times for the Oswalds, but they weren’t without hope. During a trip to the Fort Worth Botanic Garden, Oswald exuded an air of optimism. He was back in America with a beautiful wife and an adorable daughter; his life ahead promised more study and a possible university degree; a publisher would surely understand the value of his memoir, and he could use it as a platform to further the socialist causes in which he believed. Marina would understand what kind of man he really was.

But over the course of those months, it became harder for him to convince her of his exceptionalism. Early that summer, Lee brought home a catalog and class schedule from Texas Christian University, and we eventually decided to drive to the T.C.U. campus so Lee could talk to a school official. He dressed for the occasion, as I remember it, in dark slacks and a white shirt, but when we arrived, he motioned for Marina and me to wait at a distance while he had a whispered consultation with the woman at a desk. They spoke for a while, but when Lee rejoined us, he was sullen and quiet. (At the time, I didn’t realize he hadn’t graduated from high school.) On other nights, the Oswalds would walk down the aisles of the inexpensive Leonard Brothers department store and whisper intently beside the produce section before a final selection was made. Lee, who controlled the budget, would then haggle over prices, particularly with meat. (He often did so, almost humorously, with a smile on his face.) We usually left with only one bag of groceries, which kept the Oswalds going for a week.

On these shopping trips, I soon realized, Marina couldn’t help noticing that other mothers were buying more, dressing better and even driving their own cars. At the same time, she seemed to be tiring of her husband’s radical ideas. During one of Lee’s lectures about Castro’s Cuba, Marina, who had lived her whole life under Communism, interrupted to say that the Soviet Union was foolishly spending its precious resources to prop up Cuba. They had so little in Minsk anyway, she said, why waste money on a faraway nation that offered her fellow citizens little besides expensive sugar? Though he constantly toted volumes about politics and eagerly name-checked “The Communist Manifesto” and “Das Kapital,” it soon became clear to me that Oswald had no real understanding of Communism beyond Marx’s appeal for workers to unite.

At the bottom of the Oswalds’ conflict, I thought, was Lee’s refusal to let Marina learn English. He argued that it would jeopardize his fluency in Russian, but more important, it was a way he leveraged control over her. During one visit to a Rexall drugstore that August, Lee became visibly angry when a pharmacist offered to hire Marina, who had worked at a hospital pharmacy in Minsk, once her language skills improved. The job, after all, could have made her the family breadwinner. That rage would resurface later that month as we exited the duplex one evening. Marina took a step backward and fell, thumping her head on the hard, dry ground and dropping June. The thud was so loud that I feared she might be seriously injured; Lee, however, screamed at her for her clumsiness as she lay curled on the ground clutching for her baby. Even after he realized June was fine, he didn’t speak to Marina for the rest of the night.

After a couple of months of lessons, my parents’ Russian émigré circle became curious about my new friends. So on Aug. 25, 1962, we invited the Oswalds to a small dinner party at our house. George Bouhe, a dapper bachelor who took it upon himself to be a one-man social-service department for new Russian-speaking immigrants, was particularly eager to meet Marina. After all, they each grew up in what is now St. Petersburg. But as a true patriot of his adopted country, he was wary of her husband for leaving the U.S. for the Soviet Union.

Soon after I arrived with the Oswalds, Marina and Bouhe repaired to the living room. He brought along maps of St. Petersburg at various stages of its history, and they spread them out on the floor and huddled together, pointing at various landmarks. Bouhe was impressed that Marina spoke educated Russian and that her grandmother had attended an exclusive girls’ school. Marina also disclosed that her grandmother was religious, which was particularly pleasing to Bouhe because he organized Russian Orthodox services in Dallas. After a short while, he concluded that he would do whatever he could for this young woman, even if that meant helping her husband, who had sulked off to the den, waiting to be called to the table.

When dinner was served, Bouhe kept things light by asking Lee and Marina about life in Minsk. Yet I recall that his companion for the evening, a Russian woman named Anna Meller, couldn’t resist asking the question we all secretly wanted answered — why had Lee defected to the Soviet Union? Lee, who had been on his best behavior and even wore a sports jacket to dinner, suddenly became agitated and defensive. His voice rose, but what came out were canned slogans — he left because capitalism was a terrible system, it exploited the workers, the poor got nothing and so forth. Meller would not let him off the hook, though. The Soviet Union was a miserable place to live, she continued, so why had he left a country that was so wonderful and hospitable? Lee responded defensively that, yes, he did not think that the party faithful believed in Communism anymore but that this did not make America a great place.

Later in the evening, Bouhe and Meller began to insist that Marina needed to learn English if she was to survive in America. In fact, Bouhe noted, he had arranged English lessons for many Russian émigrés; he could do the same for her. Now Lee’s voice rose again. If he allowed Marina to learn English, he said, his Russian would suffer, and it was very important that he retain his fluency. Anna Meller could scarcely control her anger over his selfish behavior. Dinner ended abruptly.

As the summer drew to a close, before I returned to Norman for my senior year at O.U., I went to the Oswalds’ for my final language lesson. Because we had never agreed on a fee for my lessons, my father and I decided to pay Marina $35. It was a considerable sum (at one time, Lee gave her $2 a week from his earnings), but she refused it immediately — friends, she said, did not accept money from one another. After I insisted, she said she had never had such a sum of money in her life and planned to go right to Montgomery Ward. As a sign of her gratitude, she gave me a memento from her days in the Communist youth league — a pin of Lenin’s image, chin jutted out in a defiant but thoughtful pose. I accepted her gift gratefully and noticed that Bouhe and Meller seemed to have provided a playpen, used clothes and other amenities in the Oswald home. (In the past, I saw baby June sleep on a blanket atop a suitcase.) I asked Marina whether she had followed Bouhe’s urgings and begun to learn English. She shrugged. She would get around to it one of these days, she said.

Two months later, I peered into the mailbox of my student walk-up in Norman and extracted a penny postcard, which had been handwritten and posted two days earlier from 602 Elsbeth Street, Dallas. “Dear Paul!” it read, “We have moved to Dallas where we have found a nice apartment and I have found work in a very nice place, we would like you too [sic] come and see us as soon as you get a chance,” before eventually signing off in Russian. I was certainly relieved to hear that the Oswalds were doing well, and I assumed, from the spelling and punctuation mistakes, that Marina had written the letter and was getting the hang of English. I wrote her a response telling her as much, politely suggesting a few points about punctuation. Marina had always seemed eager to impress on me the finer points of grammar during our Russian conversations. I assumed she would appreciate the thought.

But a week and a half later, after I returned to my parents’ home for Thanksgiving, I answered our single phone at the bottom of the staircase. Marina, who was calling from Robert Oswald’s house in Fort Worth, said immediately: “I did not write that letter. Lee did.” Her tone told me all I needed to know; Lee had been deeply insulted and mortified by my response. Marina then told me she was unhappy. She hinted at physical abuse and explained that she had left him only to reconcile after he pleaded for her to attend Thanksgiving at his brother’s house. For the time being, he was treating her better, but she did not know for how long. Would I mind coming over? Perhaps a visit might remind them of better times.

I arrived at Robert’s house as the guests were leaving and then drove Lee, Marina and June back to our house. We said hello to my parents and went into the kitchen to prepare some turkey sandwiches. I tried to keep the conversation casual, but Marina began complaining about Lee even as he sat beside her, largely silent. He treated her Russian friends poorly, she said, and tried to keep her isolated in the house, doing the grocery shopping himself. I listened uncomfortably, sensing his hostility at me for suggesting that he, a self-styled intellectual keeping a “Historic Diary,” could not write or punctuate any better than someone just learning English. After an hour or so, I drove them downtown to the bus station for their ride back to Dallas. Marina waved goodbye from the steps. It was Nov. 22, 1962. I never saw them again.

On the Saturday morning after Kennedy was killed, I was sitting in my small apartment in Norman when a Secret Service agent and the local chief of police arrived and took me some 20 miles down I-35 to Oklahoma City for questioning. As we drove, I began telling them about how I met Oswald, the evenings driving around Fort Worth, the Dallas Russians and how a college kid got caught up with an accused assassin. After they escorted me into a nondescript conference room in a downtown building, the agents homed in on the question of the day, which, of course, has lingered over the past 50 years: Did I think Oswald worked alone or was part of a larger conspiracy? I told them simply that, if I were organizing a conspiracy, he would have been the last person I would recruit. He was too difficult and unreliable.

Over the years, despite public-opinion polls, many others have agreed. The opening of formerly secret archives in Russia indicate that the K.G.B. didn’t want to recruit Oswald. Cuban intelligence officers, a K.G.B. agent or two, Mafia bosses and even C.I.A. officers (including, supposedly, members of Nixon’s “plumbers” team) have somehow been tied to Oswald’s actions that day, but it’s difficult to understand how these conspiracy theories would have worked. Oswald, after all, fled the Texas School Book Depository by Dallas’s notably unreliable public-transportation system.

It’s discomfiting to think that history could have been altered by such a small player, but over the years, I’ve realized that was part of Oswald’s goal. I entered his life at just the moment that he was trying to prove, particularly to his skeptical wife, that he was truly exceptional. But during those months, his assertion was rapidly losing credibility. Marina would later tell the Warren Commission, through a translator, about “his imagination, his fantasy, which was quite unfounded, as to the fact that he was an outstanding man.” Perhaps he chose what seemed like the only remaining shortcut to going down in history. On April 10, 1963, Oswald used a rifle with a telescopic sight to fire a bullet into the Dallas home of Maj. Gen. Edwin Walker, the conservative war hero, narrowly missing his head. Oswald told his wife about the assassination attempt, but she never told authorities before Kennedy’s death.

Seven months later, a far greater target would be scheduled to pass by the very building where he worked. As Priscilla Johnson McMillan writes in her book, “Marina and Lee,” the president’s route under Oswald’s workplace might have convinced him that fate had provided a unique opportunity. “The whole series of frustrations had now brought him to this final stage,” Robert Oswald writes in his memoir. “The discouragements and disappointments beginning in his childhood, continuing through the school years and the years in the Marines, the death of his dream of a new life in Russia, the boring jobs back in the United States, which made it impossible to support Marina adequately and gain some recognition as a man . . . the whole pattern of failure throughout most of his 23 years led to the outbursts of violence in April and the final tragedy in November 1963.”

Robert Oswald told me in September that he had not talked to Marina in quite a while. When I reached him by phone at his home, he had the wary tone of a man who has spent half a century answering for someone else. He recalled my father fondly (“Pete Gregory was a good guy,” he said) but politely refused to recount his experience yet again. Agent Mike Howard of the Secret Service told me he had not spoken to Marina since the exhumation of Lee Harvey Oswald’s body in 1981. But he recalled with clarity the frantic image of Marguerite Oswald roaming around the suite at Six Flags; he also remembered that she hid a bayonet under a pillow.

Two years after the Kennedy assassination, Marina married Kenneth Porter, an electronics technician who has effectively protected her from the media. They had a son and now live in a central Texas town, not far from Dallas. This summer, with the 50th anniversary of the J.F.K. assassination looming, I sent Marina a personal letter and a written recollection of our time together and followed up this fall with a phone call. Her husband answered and confirmed that Marina had received the package but said that she had not read my reflections and did not wish to speak. Their son,