Jolanta Topolska, 53, and Tsvetanka Kostadinova, believed to be in her early to mid-30s, were two of the victims, the Tribune reported. Relatives identified the third victim as David Hanik, 61, of Arlington Heights. Hanik's brothers, Ron and Rich, identified him to the Tribune. A 65-year-old woman and a man in his early to mid-40s were also killed but have not yet been publicly identified, the newspaper reported.
Crosses set up in front of the building identified two of the victims as Danail Mladenov and Ivaylo Popov, WBBM reported.
According to a tweet from Chicago police, the incident was the result of a dispute between Marek and his neighbors, the television station reported.
Police said Marek, a retired construction worker and a former president of the condominium's association, opened fire with a handgun around 5:30 p.m. Saturday, WGN reported.
"When he walked into that neighbor's apartment, there were four people at the table eating dinner. For reasons we don't yet know, he opened fire on all four of those individuals, killing them all," Chicago Police First Deputy Superintendent Anthony Riccio told the television station.
After that, police said Marek went upstairs to the third floor of the condominium and fatally shot another woman.
According to a police report, officers encountered Marek outside the condominium with his arms raised, the Tribune reported. He then allegedly led police to a handgun in his living room, the newspaper reported.