Mad Dog(1980)

Original title: Wściekły

Detective thriller about a killer loose in the crowds. The film follows a sniper on his rounds looking for victims, while a police inspector, with few clues in hand, has to figure out the motive for the killings as well as who the psychopath is and where he might strike next. He uncovers that the mentally deranged sniper can't stand seeing people happy together in public places.