Once, during a conversation about medical school, Dan smiled and told me he would title his application essay, "From Killer to Healer." He seemed to be coming to terms with and atoning for a violent past. And yet, in retrospect, it now seems obvious that violence and rage were part of his make-up, something he couldn’t escape.

In 1990 and 1991, Dan came to my parents’ home in New Haven, Connecticut, for several family functions. On one occasion — it may have been Thanksgiving — he sported a shiner under one of his eyes. He had gotten into a fight with several Dartmouth basketball players, men much taller than he. What prompted the fight I don’t recall, but I do remember that Dan had been angry about an editorial on Israel in the Dartmouth student paper and had replied with a strong letter to the editor.

Another memory stands out more clearly. Dan had just returned from a visit with Julie in Manhattan; she was taking classes at Columbia University. He told me that it "wasn’t good for him" to be in New York. He explained that there were too many people around and that they would bump into him. I didn’t think much about his words at the time, but it’s clear to me now that Dan was a man who needed his space.

During this time, Dan wrote short stories; he said that he would submit them for publication only if he knew they would be published. He added, "I only go for a sure thing." Those words later resonated for me as Dan’s relationship with Julie grew troubled. He loved her, thought of her as a sure thing. Indeed, they became engaged and both talked of becoming doctors. However, Julie also began complaining to me privately that Dan had difficulty managing his anger.

In the summer of 1992, roughly a month after their engagement party, I picked up Julie and Dan in Worcester, and we drove to Boston for a double date. I was friendly at the time with a young woman also named Julie, a BU undergraduate.

After I rang the bell at Julie’s Allston apartment, we waited for a number of minutes. I remember how kind and understanding Dan was. Sensing that Julie might be standing me up, Dan said that we would go out to dinner no matter what. A little while later, Julie opened the door, and we left for the North End. We had a lovely meal at an Italian restaurant. The vibes were all good, and afterward we went to a pastry shop for dessert. As I recall, we waited a long time for our order, and then the waitress brought us the wrong item. This enraged Dan, who jabbed his finger at the server and yelled, "I’m talking to you!" as she walked away. This was no playful riff on Robert De Niro’s famous, "You talking to me?" routine in Taxi Driver — Dan was serious.

My cousin Julie looked at me and rolled her eyes as if to say that she had to deal with this on a regular basis. My date looked down at the table. I tried to calm Dan, assuring him that everything would be all right. But we were all stunned by his outburst.

Another time, in 1992, I visited Julie and Dan at their apartment in Worcester. I had always been good at arm wrestling and typically challenged men bigger than I. Though Dan was a smaller man, because of his vaunted military background I challenged him to a match. I suppose that I wanted to prove myself to Dan in a physical way, wanted him to respect my strength, just as I respected his. He declined the match. I told him that he would "probably kick my ass." He said, "No, you would probably kick my ass, and that would not be good."

As I look back on it now, Dan obviously knew his limits, his explosiveness, knew that even an arm-wrestling match was dangerous for him and his opponent. As for the road-rage incident in which Dan crossed paths with Eugene Yazgur, I can easily imagine how Yazgur might not have understood the peril he was in.

THE SECOND day of the trial features the dramatic appearance of Yazgur, the intended target of Dan’s murderous rampage, according to the prosecution. Yazgur, who has undergone 17 surgeries, walks with the aid of a cane and with braces strapped around both legs. He wears a harness on his right arm for support. His face has been sewn up since he took a bullet in the mouth. That bullet, the first one fired at him, smashed his nose, exploded through the roof of his mouth, pierced his tongue, and exited his lower jaw before lodging in his chest.

He lost five teeth in the shooting, but he can still eat solid foods: in the cafeteria, I saw him carefully remove the harness from his arm to dip his hamburger and French fries in ketchup. A Russian immigrant, Yazgur speaks good English, but with his accent, ruptured tongue, and missing teeth, it is sometimes hard to understand him. Judge Christine McEvoy asks him to repeat his words when he says that after Mason assaulted him in 1997, he "looked like Evander Holyfield when he fought Tyson." This was a reference to how his ear lobe hung from the side of his head after Dan slashed him with a knife; 30 stitches were required to sew it up.

Yazgur’s testimony takes up the better part of two days. Throughout this period, he rarely looks at Mason, though no barrier prevents it. As Wall finishes questioning Yazgur, he asks him to indicate Mason to the jury. At this moment, Yazgur points and stares right at the defendant. Mason turns away and does not meet the victim’s gaze.

As I watch Mason being cuffed again for his return to jail, he strikes me as a caricature of a mob enforcer: a short, wide-bodied man, with a bloated face. I can see now that he could have been a bodyguard, the career he had considered in Israel.

Outside the courtroom on the first day of the trial, I ask Dan’s mother, a warm, roundish woman, about Dan’s early years in Israel. She tells me that as new immigrants, olim chadashim, they lived in subsidized housing in Jerusalem and other towns. Young Dan was "very close" to his then-stepfather, Beverly’s second husband, an Israeli soldier who died in an accidental shooting. At 13, Dan moved to a kibbutz and lived with a kibbutz family rather than with his mother.

After she tells me this, her son, Ben Chafetz, admonishes her in Hebrew. She says that she can no longer talk to me about Dan. Ben, whom I had met years ago at Dan’s engagement party but who does not recognize me, tells me that he doesn’t really like journalists; the press, he says, has "vilified" his brother.

THE FOURTH day of trial is filled with exhibits, primarily photographs of the apartments in which Mason and the victims lived. The exhibits now total more than 100. Wall shows each image on a screen and methodically questions Detective Paul McLaughlin about each bullet hole and shell casing. At one point, Mason and his attorney, Jubinville, huddle over photos of Mason’s former Malden residence. Mason’s mustard-green suit creases across the back. He may be straining to fit into it; at one point I overhear Jubinville tell the bailiff that Mason may have lost weight during his incarceration, but Mason’s girth has increased since he last wore this suit.

Later on, the two attorneys meet with Judge McEvoy for a protracted sidebar on the admissibility of questioning Francis DelloRusso, Mason’s former landlord, about "charred" pieces of paper retrieved from the furnace in Mason’s former apartment building. During the conference, the beefy bailiff struts around the court. Sticking out his chest and with clenched teeth, he asks Mason if he wants water and then pours him a paper cupful from a thermal pitcher. The bailiff, who talks and looks like Robert De Niro in GoodFellas, then congregates with the other court officers standing near Mason. It is a fitting tableau of two De Niro characters — the defendant, a prospective bodyguard who once unknowingly emulated De Niro in Taxi Driver, and the wise-guy bailiff standing behind him against the bar enclosure.

IN AUGUST of 1992, I visited Julie and Dan in Worcester. Dan was having trouble studying for the MCATs. He told me that he had a learning disability and needed extra time to take standardized tests. He and Julie asked if I would help him prepare. Unfortunately, I was not sensitive enough to Dan’s needs, not sufficiently patient as we studied math together. Later, while we brunched on bagels and cream cheese, Dan made a disparaging remark about my lack of fluency in Hebrew.

That was the last I saw him.

Months afterward, I learned from my cousin that Dan had erupted violently — cursing and yelling — while driving in traffic. For Julie, it was the culmination of many frightening episodes, and she called off their engagement. Dan’s response was much more harrowing: he broke into Julie’s home and threatened to kill her and her family. They obtained a restraining order against him, and Julie went into hiding.

Strangely enough, despite Dan’s violence toward my cousin, I felt compassion for him. He was a very modest-looking man who had managed to find the woman of his dreams — only to lose her.

As the prosecution winds up its case, I too feel a sense of loss. The jury will likely render a verdict in the next few days. I suspect that he is guilty. Of course, I may be wrong about Dan’s guilt, but I have forever lost a friend, a man I once admired, a man whose rage turned deadly.

Robert David Jaffee is the author of Strikeout at Hell Gate (1st Books, 1998), a novel about baseball. He is on staff at the LA Weekly and can be reached at rjaffee@laweekly.com