CHICAGO (CBS) – There are still few clues in the murder of Chicago Police Officer David Blake. He was shot to death in his SUV Monday night while he was off-duty. Visitation for Officer Blake was held on Sunday.

CBS 2’s Vince Gerasole reports that a steady stream of officers and family members passed into the Leak Funeral Home on the South Side on Sunday afternoon to pay tribute to Officer David Blake.

Blake was most recently a SWAT officer, and many SWAT team colleagues came by in their fatigue uniforms to offer their respects.

Sources say the 45-year-old was shot five times in the head while off duty. His body was discovered in his car in the 2900 block of west Seipp Street on Monday.

Dozens of people have been questioned in the murder, but so far no arrests have been made.

Blake’s former partner and friends commented on how his violent death, and that of another officer on Friday, is impacting the force.

“What this will do is boost morale. This makes you want to go out here and get the bad guy,” said Officer Sean Davis, Blake’s former partner. “Until we figure out who’s doing these crimes against police, this reinforces our effort to go out here and do what we gotta do.”

“It’s difficult but it’s a job we have to do and we’ll continue to do it,” said Officer Sam Kendrick, Chicago Police Dept.

Also present Sunday were members of the CPD Gold Star Families, with a plaque paying tribute to officers killed, many in the line of duty.

They say their frustrations lie in an understaffed police department.

“The police need to be able to be the police. We have a weakened department and these gangbangers know it, and these people with evil intentions know it,” said Donna Marquez, president of Gold Star Families. “And the department needs to get together and be stronger. Our leadership needs to take care of our officers. That’s why the morale is the lowest as it’s ever been.”

Visitation for Officer David Blake wrapped up at 5 p.m. Sunday. Funeral services will be private.