It happened around 9:40 p.m. Wednesday on the unit block of Balfour Avenue in Claymont.
Arriving officers discovered a 27-year-old male and a 16-year-old male shot inside a car. They found a 19-year-old female victim outside the vehicle.
First aid was provided at the scene by officers and medics.
All three were taken to a hospital. The two males were pronounced dead.
Later, police said an additional 18-year-old male victim suffering from a gunshot wound arrived at a hospital via a private vehicle.
Investigators determined that this male was also shot on Balfour Avenue during the same incident.
The 19-year-old female and 18-year-old male are listed in critical condition.
Detectives from the New Castle County Division of Police Criminal Investigations Unit are conducting the investigation.
Anyone with information and/or video pertaining to this investigation, should contact Detective Kevin Mackie at 302-395-8133. You can also contact the New Castle County Division of Police non-emergency number at 302-573-2800.