Saying that Ronell Wilson “has earned the ultimate punishment,” a federal prosecutor called for the killer of two undercover detectives to be put to death.

“You are here to decide the right punishment for a cold-hearted, remorseless, double murderer,” Assistant U.S. Attorney Morris Fodeman told a federal jury in U.S. District Court in Brooklyn.

“The death penalty is the right penalty,” he said.

The jury weighing Wilson’s fate last month convicted the 24-year-old defendant of five counts that carry the possibility of a death sentence. The crime is the 2003 murder of two detectives in the NYPD’s Firearms Investigation Unit, Rodney Andrews and James Nemorin. They were killed as they tried to purchase a gun from Wilson during a police sting operation in Staten Island.

Mr. Fodeman told the jury of the devotion Andrews had for his two children and the love Nemorin felt for his three.

“They deserved to live,” Mr. Fodeman said of the detectives. “The government submits that the defendant does not.”

A lawyer for Wilson began the defense’s case by saying how little, in his estimation, a death sentence would accomplish.

“More death gives only honor to revenge,” the lawyer, Mitchell Dinnerstein, said. “Honor life, vote for life,” he told the jury.

Wilson’s legal team is expected to spend several days next week calling forward witnesses who will testify about Wilson’s childhood. Wilson grew up largely parentless in Queens and Staten Island.

“Violence, drug addiction, and chaos were his constant companions,” Mr. Dinnerstein said of the surroundings into which Wilson was born. “He knew nothing else.”

Mr. Dinnerstein described his client as “a suicidal six-year-old” who was placed in a psychiatric institution after his teachers heard him talk of killing himself. He said Wilson continued to suck his thumb through adolescence.

Relatives of Andrews, including his widow, MaryAnn, told the jury of how the murder affected her. Prosecutors spent much of yesterday afternoon calling witnesses who could describe Wilson’s earliest brushes with the law.

Indeed, the circumstances surrounding Wilson’s first arrest, at age 11, seemed to carry a vague omen of the crime for which he now faces sentencing.

Wilson’s first arresting officer, Paul Alaimo, testified that he still remembered how Wilson had hurled a bottle at his police van 13 years ago. Mr. Alaimo testified that he chased Wilson and arrested him.

“I happen to remember this very clearly because I had never arrested an 11 year old,” he explained to the jurors.

Mr. Alaimo testified that as he drove Wilson back to the stationhouse after the incident he asked the boy a question: “Today you’re throwing a bottle at us, what’s going to happen when you’re older, are you going to shoot at us?”

Wilson gave no answer, Mr. Alaimo said.