A federal prosecutor told a jury yesterday that the Staten Island man accused of executing two undercover detectives during a gun sale in 2003 had considered that his victims might be police and simply “did not care.”

The defendant, Ronell Wilson, now 24, could face the death penalty if convicted in a trial that opened yesterday in U.S. District Court in Brooklyn. But the judge, Nicholas Garaufis, instructed the 12 jurors and six alternates not to think about sentencing Mr. Wilson during the first stage of the trial, as they decided the factual question of his guilt or innocence of the federal racketeering crimes he is charged with.

Mr. Wilson is a reputed leader of the Stapleton Crew, a gang named after the Staten Island housing project of the same name. Mr. Wilson is accused of killing detectives James Nemorin and Rodney J. Andrews as he gave them driving directions from the back seat of the car.

The car, a Nissan Maxima, is at the center of the case. The ride began at about 7:15 p.m. on March 10, 2003, when the detectives pulled up in front of Wilson, then 20, and his 17-year-old associate Jesse Jacobus at the housing development.

The aim of the detectives, both members of the elite Firearms Investigation Unit, was to purchase a TEC-9 submachine gun for $1,200 and get “one more gun out of the hands of one more violent criminal,” an assistant U.S. attorney, Colleen Kavanagh, said. A half-hour later, the bodies of detectives were found in a nearby street. Both men had been shot in the head.

The conversation from the final 30 minutes of the detectives’ lives was captured on a static-filled audiotape that prosecutors played yesterday. The conversation between Mr. Wilson and the detectives was fueled by suspicion. Mr. Wilson had expected only one man, not two, to show up for the deal. Nemorin repeatedly tries to allay Mr. Wilson’s suspicions by saying Andrews is his brother-in-law.

Sometime before the shootings, Ms. Kavanagh said, Mr. Wilson’s plans changed, from wanting to sell a gun to aiming to murder and rob his prospective buyers.

“During the planning of the robbery, the group discussed at one point whether or not the Haitian was an undercover police officer,” Ms. Kavanagh said, referring to Nemorin, who had bought a gun from the Stapleton Crew before and had identified himself as “a Haitian from Brooklyn.”

“The evidence will show, ladies and gentleman, that the defendant did not care,” Ms. Kavanagh said.

It was for the purpose of robbing the detectives that Mr. Wilson gave Nemorin, who was at the wheel, circuitous driving directions, Ms. Kavanagh said.

“Wilson wasn’t directing them where to go to buy a gun, he was directing them to go where they would be murdered, Ms. Kavanagh said.

Mr. Wilson, held in custody since two days after the murder, was quiet throughout most of yesterday’s proceeding. He did not wear a coat or tie, and sat perfectly still for much of the day.

Mr. Wilson’s attorney, Ephraim Savitt, told jurors that Stapleton Crew members who would testify against Mr. Wilson could not be trusted to prove that he was the triggerman.

“The government’s case is literally permeated with reasonable doubt,” Mr. Savitt said.

Mr. Savitt sought to cast doubt on whether Mr. Wilson was actually in the back seat of the car at the time of the execution-style killing, which the prosecution has described as occurring at such close range it produced muzzle burns.

About 15 minutes after the defendant and Mr. Jacobus, his accomplice, got into the car, Mr. Wilson got out to get the handgun that he would use to murder the detectives, prosecutors say.

After questioning by Mr. Savitt, the commanding officer of the two detectives, Sergeant Richard Abbate, told the jurors that he did not see who was in the car when it took off again after the stop.

Sergeant Abbate had been trailing the detectives in a sport utility vehicle and listening to the receiver that picked up the conversation from Nemorin’s car. When the recording began to grow more static-filled, Sergeant Abbate tried to call the detectives on their cellular phones, he said.

“I was repeatedly calling them, mostly trying to get in touch with Andrews because he was the passenger,” Sergeant Abbate told the jurors. “I never got in touch with either one.”