CHICAGO (AP) — A Chicago man who gunned down five of his neighbors over the weekend had angry run-ins with his fellow tenants and left cryptic notes on his door suggesting he was planning an act of violence, authorities said Monday.

Investigators still haven’t determined the exact reason why 66-year-old Krysztof Marek shot four neighbors as they were sitting down for dinner on Saturday before chasing down a fleeing woman who lived upstairs and shooting her in the head outside of the building on the city’s northwest side, police said.

During a hearing Monday in Cook County Circuit Court, prosecutors said they found two threatening notes written in Marek’s native Polish language that were taped to his apartment door.

Police spokesman Anthony Guglielmi said Marek had previously confronted his neighbors over what he called petty matters, including telling off a woman who angered him because he felt she was walking too loudly on the floor above his apartment.

After the shootings, Marek put the .40-caliber handgun on a coffee table in his apartment, walked outside and told police when they arrived, “I think you’re looking for me. I did it.”