Superintendent says the two knew each other and may have lived together.
Bernard Williams, 18, is accused of killing Blake in order to obtain his extensive gun collection, police supt. Jody Weis said at a Thursday morning press conference announcing the arrest.
"Because our officers were stationed at Blake's home immediately after the incident he wasn't able to gain access to the house using the keys he stole," Weis said.
Williams may have lived with Blake for a short time, and lured him to the dead-end street to discuss moving back in, according to sources. Weis wouldn't confirm or deny that development.
"They knew each other," he said. "They may have lived together at one point. ... They were meeting that night to discuss hooking up, you know, to watch a football game or something."
Authorities said Williams is a Ganster Disciple gang member.
Blake, a 15-year veteran, was off-duty when he was gunned down in his SUV in the 2900 block of West Siepp Street on Nov. 22. His wallet and service weapon were found nearby, authorities said.
He was the fourth police officer killed by gunfire this year. Another officer, 46-year-old Michael Flisk, was gunned down just four days after Blake.
Officer Thor Soderberg was shot and killed by a man in early July. Two weeks later, Officer Michael Bailey was gunned down on the South Side as he returned home from a shift guarding Mayor Richard Daley's home.
Officer Thomas Wortham was shot and killed outside his father's home by three assailants in May.
Another officer, Alan Haymaker, was killed in a car crash while responding to a burglary call.