An accomplice of convicted cop-killer Ronell Wilson testified at his death penalty retrial on Tuesday that the gang member coldly ignored cries for mercy as he held a gun to the head of undercover detective James Nemorin of Baldwin Harbor after killing his partner.

"He started pleading," accomplice Jessie Jacobus, 27, who was with Wilson as the undercover gun buy in 2003 exploded into violence, testified in Brooklyn federal court. "Don't shoot! I got a family! I got a family! Don't shoot!"

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Wilson's response was to pull the trigger, Jacobus said in a reprise of his testimony at Wilson's first trial in 2006. That jury sentenced Wilson, 31, to death for murdering Nemorin and partner Rodney Andrews in Staten Island, but an appeals court ordered a retrial of the penalty phase of the case.

In his only new testimony, Jacobus, who was sentenced to 15 years to life for his role after agreeing to testify for the government, said that Wilson tried to recruit him to help with his death penalty defense in a chance meeting on an elevator in jail in 2011.

"He asked me to tell the prosecutors that we had a rough upbringing," said Jacobus, who like Wilson had a crack-addicted mother, an absent father and grew up in poverty in Staten Island's Stapleton Houses.

Wilson's primary argument to the jury has been that his criminal responsibility is mitigated by the scars of abuse and neglect he suffered as a child. But when defense lawyer David Stern on cross-examination suggested to Jacobus that family circumstances were responsible for his own life of crime, Jacobus rejected the idea.

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"It still doesn't cause you to commit murders," he shot back. "I chose to live a certain lifestyle not because of that. I chose to run the streets and do crimes."