A federal jury in Brooklyn begins deciding today whether to sentence to death a man convicted of killing two police officers.

The jury’s task starts with a comparison of two lists. One list, supplied by the defense, lists 19 reasons to spare the life of Ronell Wilson, 24, who shot the two undercover detectives in the head on March 10, 2003. The other list, supplied by the prosecution, contains six reasons to sentence him to death.

The instructions the jury will receive place these competing factors at the center of its decision-making process.

“This court will instruct the jury … that the process of weighing the aggravating and mitigating factors against each other in order to determine the proper punishment is not a mechanical process,” the judge, Nicholas Garaufis of U.S. District Court in Brooklyn, wrote in an order on Friday that lays out the jury instructions he intends to give today. “Rather, the court will instruct, the jury should consider the weight and value of each factor found to exist.”

Prosecutors say Wilson deserves the death penalty because he killed two people, not one, and because both victims, James Nemorin and Rodney Andrews, were New York City police officers. Prosecutors have also offered as an aggravating factor the impact the crime has had on the wives of both men and the five children who were left fatherless.

Against these aggravating factors, the defense submitted a list of 35 mitigating factors, which Judge Garaufis edited down to 19. Several of the mitigating factors relate to the defendant’s childhood in Brooklyn and Staten Island, including Wilson’s bout of bacterial meningitis as a toddler and his early years of “poverty and deprivation.”

It is possible, even likely, that these aggravating and mitigating factors will serve only as a starting point for the jury, which is set to begin deliberating this afternoon, after lawyers for both sides give closing remarks this morning.

Indeed, the thoughts of jurors are certain to turn inward, as each examines his or her own notions of what justice does or does not demand in Wilson’s case.

“Beyond that, it is no longer a formulaic approach,” one of Wilson’s attorneys, Ephraim Savitt, said. “It’s now a decision the jurors decide based on their own moral judgment, really.”

A death sentence requires a unanimous vote from the jury. If the jury does not agree on death, Wilson will be sentenced to life in prison. Although no federal jury in New York has imposed a death sentence since the federal death penalty was reinstated in 1988, Wilson is readying himself for the possibility of a death sentence, Mr. Savitt said.

If Wilson is sentenced to death, he will be executed by lethal injection. Wilson, Mr. Savitt said, is aware of the dispute over whether excruciating pain accompanies a lethal injection.

“He’s concerned about the death penalty, lethal injection, and the pain it could involve,” Mr. Savitt said. “He’s read about it on his own.”