(CNN) -- Seven people were found shot to death Sunday inside a Grapevine, Texas, apartment, police said.
The seven, believed to be related, were apparently in the process of opening Christmas gifts or had just finished doing so in the apartment's living room area, said Grapevine police Sgt. Robert Eberling.
Authorities responded to the address "in reference to a 911 open line," Grapevine police said in a statement.
The seven bodies -- four female adults and three adult males -- were found when officers entered the apartment. "All victims appear to have gunshot wounds," said the statement.
Authorities are not searching for a suspect, said Eberling, and believe one of the seven people was the shooter.
The victims range in age from about 18 years to middle age, he said.
The investigation was ongoing, authorities said.
Grapevine is about 25 miles northwest of Dallas.
CNN's Chuck Johnston and Darrell Calhoun contributed to this report.