GRAPEVINE, Texas — Police in a quiet Fort Worth suburb worked Monday to piece together a family history after a man dressed in a Santa Claus suit apparently shot six relatives and himself on Christmas.

Grapevine police spokesman Sgt. Robert Eberling said the shooter showed up in the costume shortly before gunfire erupted and that the family appeared to have been opening Christmas presents. Police responding to a 911 call found four females and three males dead. They also found two handguns.

'We think he was just inside there celebrating Christmas with the rest of them and decided for whatever reason that's how he's going to end things,' Eberling said.

Investigators worked through Sunday night and into Monday morning, meticulously searching the apartment where the bodies were found, along with vehicles parked outside. Police said they think the victims were related, though some were visiting and didn't live in the apartment.

Eberling said investigators were assembling a 'family history,' and that the apartment was leased to a woman and her two children, one age 15 and the other either 19 or 20. He would not give other specifics.

'We're getting a clearer picture, but we're not ready to go on the record with anything until we find out from the medical examiner absolute confirmation of identities and the manner of death,' Eberling said.

Autopsies of the shooter and the victims were being done Monday by the Tarrant County medical examiner, but it would probably be today before their identities were released, he said.

Roger Metcalf, a spokesman for the medical examiner's office, said the victims have been tentatively identified, but the office couldn't confirm the names because the state driver's license fingerprint database wasn't available on the holiday. 'In addition, we need to locate next of kin before information can be released, and our investigators are working on that as well,' Metcalf wrote in an email to the AP.