MILWAUKEE (CBS 58) -- Milwaukee police are investigating a quadruple shooting that happened on Saturday, July 6. 

It happened near Dr. Martin Luther King Jr Drive and 6th around 1:30 a.m. 

Milwaukee police say a 17-year-old sustained life-threatening gunshot injuries and was transported to a local hospital. 

A 15-year-old sustained a non-life-threatening injury and was taken to a local hospital. 

The third victim, a 21-year-old, also sustained a non-fatal gunshot injury and was transported to a hospital. 

The fourth victim, an 18-year-old, sustained non-fatal gunshot injuries and went to the area of Port Washington and Richter, where medical attention was summoned, and was transported to a hospital. 

The circumstances leading up to the shooting are under investigation. Milwaukee Police continue to seek unknown suspects.

Anyone with any information is asked to contact Milwaukee police at (414) 935-7360 or to remain anonymous, contact Crime Stoppers at (414) 224-Tips or P3 Tips.