NEWARK  Returning to New Jersey for his 30th high school reunion, DeFarra Gaymon had the kind of life one would not mind describing to old friends: he was a C.E.O., married, father of four. But Mr. Gaymon, who was in the Chess Club, the French Club, the Italian Club and the student coalition at Montclair High School, never made it to the party on Friday night at the Crowne Plaza Meadowlands.

Instead, as other members of the class of 1980 were collecting their name tags, Mr. Gaymon, known as Dean, lay dying at the University Hospital in Newark, having been shot in the chest by a police officer in Branch Brook Park, a few miles away.

On Tuesday, the acting Essex County prosecutor gave the first detailed, public description of what happened in the wooded park that night, saying that the officer, who had tried to arrest Mr. Gaymon, 48, over lewd behavior, fired in self-defense. The prosecutor, Robert D. Laurino, said that Mr. Gaymon assaulted the officer, a 29-year-old member of the Essex County Sheriff’s Department, tried to flee and then, when cornered, attempted to disarm the officer.

Mr. Gaymon’s family released a statement that said, in part, “We know that the police killed an innocent man, with no history of or disposition towards violence.” A man who answered the phone at the family’s home in Suwanee, Ga., said no one there had more to say.