Four people were killed in a shooting at a house in Aurora, a city in the US state of Colorado, with the suspect still at large, local police said.
In a statement on Sunday, the Aurora Police Department (APD) said it received a report of a shooting at the house downtown at roughly 2 a.m., reports Xinhua news agency.
Officers found four adults, three men and one woman, dead from gunshot wounds when they arrived three minutes later.
The suspect was identified as Joseph Castorena, 21, supposedly the domestic partner of the woman killed in the house.
A relative of the dead woman told local MSNBC 9 news channel that it was an ambushed shooting.
The suspect hid in the house and opened fire when the victims returned from a party.
Shortly after the shooting, a reverse 911 alert was issued in a one-mile radius for all residences to shelter in place, while officers searched the neighbourhood in the dark.
The APD classified this investigation as a homicide case but warned the suspect was dangerous and may have a gun.