But investigators were still working out the full time line of the massacre, the worst in the town's history, Grapevine police Lt. Todd Dearing told the Fort Worth Star-Telegram.
Police said the victims were found beside open gifts near a Christmas tree in the apartment, the report said. Two handguns were found at the scene.
Dearing said all seven of the dead were "related either by blood or by marriage."
Investigating officers went to the apartment about 11 a.m. Sunday after receiving an emergency call from the home, The Dallas Morning News reported. Police said no one was on the line when the 911 operator answered the call, the newspaper said.
Police said the victims included four women and three men who were found in the living room and adjoining kitchen, and it appeared all the victims had been shot, with the shooter among them.
The slayings were the first this year in Grapevine, a Dallas-Fort Worth suburb of about 46,000 people.