By Vi Nguyen

CHICAGO (CBS) — A west suburban cigar lounge will re-open Monday, just three days after a shooting left a retired Illinois state trooper dead and two others hurt.

CBS 2’s Vi Nguyen reports, investigators are now trying to determine a motive for the shooting.

The Humidor Cigar Lounge has been closed since the shooting Friday night, but doors will open again around noon. Outside the lounge you can see a memorial for the retired trooper killed and a message that reads “rest in peace.”

Investigators still have a lot of questions about the shooting suspect, 51-year-old Lisa McMullan and what drove her to shoot and kill retired Illinois State trooper Gregory Rieves.

Both have been to the cigar lounge on Odgen Avenue many times before. Investigators say McMullan knew Rieves but they don’t know the extent of the relationship.

Patrick Carlin was at the lounge Friday night playing pool and having cigars with friends when he heard gunshots coming from the media room.

“The first one sounding like a bang, like something had fallen,” Carlin said. “And then I think after the third shot, there was screaming.”

Carlin said he and his friends left, they called 911, and came back to learn a woman now identified as McMullan shot three people before turning the gun on herself.

“I couldn’t believe it. Because I know her. I mean every time I’ve gone to the lounge I would say she was there all the time so I didn’t know her personally at all. I know who she was,” Carlin said.

He added that McMullan was social with people. He even heard her laugh just 30 minutes before the shooting.

“I knew she was there when we were sitting watching TV because I could hear her laughing in the back room she has a really distinct laugh so I knew who she is,” Carlin said.

Investigators plan to interview the two surviving victims Monday. Both have been recovering from surgeries in the hospital.