It happened around 3:50 p.m. Monday at the Harbor Club Apartments near Route 4 and Cheswold Boulevard.
Officers arrived to find a man believed to be in his 30s, with a gunshot wound to the chest. He was found in cardiac arrest, and medics worked to resuscitate him.
He was taken to Christiana Hospital in critical condition where he later died.
Another male, believed to be in his 20s, was shot in the head. Paramedics transferred him to Christiana Hospital in serious condition.
Authorities are searching for a male who was seen running through the complex.
No word on what led to the shooting.