By Tommy Hallissey

Bronx homicide prosecutor David Greenfield knows people.

He knows if he can get a drugaddicted witness to confide why she uses, he can humanize her to the jury. He knows how to get a hardened criminal to snitch. But most importantly, he knows how it feels to get a Christmas card from a victim's mother 15 years after the trial.

On Nov. 29, the New York City Bar Association honored Mr. Greenfield, a 27-year veteran from Riverdale, with the Thomas E. Dewey Medal for a lifetime of service in the Bronx district attorney's office.

Recently reflecting on his tenure in the Bronx, Mr. Greenfield, 55, boasted of not only the defendants he put behind bars, but also of cases that never materialized. "I am equally proud of the cases that never went to trial and innocent people got to go home for the holidays," he said.

Mr. Greenfield, a graduate of JHS 141, specializes in cold case homicides. He has taken up cases as old as 16 years. Mr. Greenfield turns the old axiom - the longer it takes to get to the trial the weaker the case - on its head. "Over time my cases get stronger because people get arrested and come forward," he said.

One cold case victory for Mr. Greenfield remains sharp in his mind - a 15-year-old homicide with one witness. Trouble was, the witness couldn't get clean.

Mr. Greenfield checked him into a rehab repeatedly; the witness checked out again and again. The witness begged Mr. Greenfield to let him pick his own rehab. Once he found the right place, the man found God and cleaned up his life. It was just in time to testify and help Mr. Greenfield win the case.

It was a victory on another front, too. After the case, the man got a job as a chef and has been clean ever since.

Mr. Greenfield, who admitted convictions are bittersweet to him, gets a phone call from his troubled witness every Christmas to say thank you.

"It's not just the conviction, but what you do for the witnesses too," he said.