Police on Tuesday hunted for a man who opened fire at a park packed with Memorial Day picnickers, killing two people and wounding three.

Hundreds of screaming people fled after the shooting Monday evening next to a playground in South Shore Park on the Lake Michigan shore.

The picnickers and the gunman knew each other, police spokeswoman Anne E. Schwartz said at a news conference Tuesday. The man had argued with the victims before firing the shots.

She said police know who the 32-year-old shooter is but would not release his identity. He fled in a vehicle after the shooting, she said.

Peter Quinones said he saw a man in a white shirt circling tables where about 10 people were seated, shooting at them with a handgun.

"At point-blank range, he was shooting," Quinones told the Milwaukee Journal Sentinel. "He was so concentrated on that table, it looked like he wanted to wipe out that whole group of people."

Police identified the victims as Raymundo Munoz-Silva, 31, and Julio Diaz-Guillen, 17, both of Milwaukee. Both were shot in the head, police said.

Three other people were injured. A 23-year-old woman who was shot in the chest and a 34-year-old man shot in one leg were both hospitalized in stable condition Tuesday. A 21-year-old man was treated for a leg wound and released.