The Chicago Tribune says the person police are questioning is a parolee who lives near the crime scene.
ABC 7 has also learned more about shooting victim Stephen Peters, a former CHA officer and veteran.
"He believed in living life to the fullest. He believed in being a happy person. He believed that being unhappy, being negative took too much. And we always, he always greeted me with a hug and a kiss because he always felt as if tomorrow's not promised," said Djana Peters, victim's widow.
Peters is still trying to comprehend how someone could have killed her husband and Michael Flisk.
Before becoming an engineer, 44-year-old Peters worked for the CHA and Robbins Police Departments and was also in the military. He loved his wife and three children and had a passion for cars.
"He loved cars. He wasn't a big money spender, but he loved his cars. He raced. He would buy them and, like buying a house, fix them up. You'd look at it and be like, 'wow, that's not the same car,'" said Peters.
After some electronics were stolen from a car peters kept in his mother's garage in the 8100-block of South Manistee, Officer Flisk arrived to gather evidence on Friday afternoon.
Both victims were armed, but it doesn't appear they returned fire. Police recovered their guns, and their wallets, at the scene.
"So it doesn't appear at this time that anything was taken off the two victims. It appears as if the individual perpetrated this crime and fled the scene immediately," said Chicago Police Supt. Jody Weis.
On Saturday, officers and volunteers passed out fliers, appealing to anyone with information to come forward.
"Clearly, everyone's upset. This is another tragic loss of not only another citizen but another one of our officers. We're doing all we can to solve this and prevent another one," said Glen Brooks, Area 2 coordinator, Chicago Police Department.
"Let me be clear. The time of talking and making excuses is over. We need to bring this individual to justice. Quite simply, we need your help," said Weis. "No family should ever have to endure this tragic loss. We will all grieve together. But let me assure you, we will not waiver from our mission to bring those responsible for these crimes to justice."
The person of interest was picked up at his home around 5:30 p.m., according to the Sun Times. They also report that he had been convicted of armed robbery and sentenced to six years in prison but was paroled on September 14th.
Flisk was the second Chicago police officer killed this week. Forty-five-year-old SWAT team member David Blake was off-duty when he was shot to death in his parked SUV last Monday. Visitation for Blake will be Sunday. No one has been charged in the killing.