Jemetric Nicholson allegedly fired the gun that killed Metra Police Officer Thomas Cook in Harvey, Ill., in 2006.
"This case never went cold. It was never forgotten. It may have taken more than we would have liked, but it was investigated very methodically," Cook County State's Attorney Anita Alvarez said.
"We never game up on them. And we are very thankful that they were able to come to this end for us," Pamela Cook, widow.
Officer Cook was shot in the head while sitting in his squad car outside the 147th Street Metra station in Harvey in September 2006. He died instantly. His .357-caliber weapon was stolen. Prosecutors say Nicholson wanted the officer's gun after losing two guns in an earlier shooting.
A second man, 22-year-old Jeremy Lloyd, pleaded guilty last month to being the lookout in the shooting. As part of his plea agreement, he offered information related to Nicholson's involvement.
Authorities say they had evidence Nicholson was involved in the case early on, but lacked eyewitness testimony until they reached a deal with Lloyd, who will testify against Nicholson after years of holding firm.
"The code of silence, the 'no snitch' rule, was alive and well in this particular investigation," said Alvarez.
Nicholson, who is already behind bars serving time for separate crimes, was denied bail in the Cook murder case during an appearance in criminal court in Markham Wednesday morning.
"It is true that the wheels of justice move slowly sometimes. But in this case, they moved deliberately and with determination every step of the way," said Alvarez.
Officer Cook was with Metra police for about three years. Prior to that, he served with the Riverdale Police Department for a decade. He told colleagues he thought being a transit cop would be a safer line of work.
"The men and women of the task force and the state's attorney's office promised to do everything in their power to bring the murderers of Officer Tom Cook to justice. In this case, a promise made was thankfully a promise kept," said Chief Tim McCarthy, South Suburban Major Crimes Task Force.
Officer Cook was the father of two young children.