Darius Sullivan was found guilty of first-degree murder, attempted murder and endangering the life of a child.
He was accused of killing Rittmanic, 49, and badly injuring her partner, Tyler Bailey, when they responded to a call at a hotel, back in 2021.
Bailey testified from his wheelchair during the trial.
Sullivan pleaded not guilty, and declined to testify in his own defense.
Both sides rested Thursday morning.
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In closing arguments, prosecutors played the police body camera video again to the jurors, which ABC7 Chicago cannot show, per a judge's order.
Prosecutors alleged Sullivan shot the officers as they confronted him at his hotel room door over a warrant, calling his actions vicious.
Sullivan's defense attorney told jurors Sullivan was defending his family that night, thinking someone was breaking into his hotel room.
Sullivan's three children, ages 2 months to 8 years old, and his girlfriend, Xandria Harris, were also in the room.
Some of the relatives and friends of Rittmanic left the courtroom during the at times graphic body camera video. Weeping could be heard in the gallery.
Bradley police speak after guilty verdict announced for suspect in officer's murder
Sullivan's attorney argued there were holes in the state's case and evidence that was missed connecting Sullivan to the crimes.
On Dec. 29, 2021 Rittmanic and Bailey responded to a call of dogs barking in a car on a cold night outside a Bradley hotel.
Once at the scene, they believed Sullivan was a guest at the hotel, and was wanted on warrants.
Rittmanic was shot in the shoulder and twice in the neck. The last two shots were fired from her duty weapon. She died of her injuries.
Bailey was shot in the forehead, and is left with permanent disabilities, ending his career as a police officer.
The jury deliberated for just over an hour before reaching a guilty verdict Thursday afternoon.
Judge reads verdict in trial for Bradley police officer murder suspect
There were 12 jurors and one alternate.
A spokesperson read a statement on behalf of both families in front of the Kankakee County Courthouse after the verdict was read.
Harris faces a separate trial for her alleged role in the shooting. A date has not been set for her case.
Sullivan's sentencing is set for November.