HOUSTON - A gunman shot five people at a home in Tulsa, Oklahoma late Saturday, killing four of them and injuring the fifth, police said.

Police sources were quoted by the Tulsa World as saying Sunday that the five people were found at the garage area, two of them already dead at the time. Among the rest, two died later in hospital while the third, a man in his 50s, was still in serious condition.

The killer hasn't been identified and was still at large.

Police identified the dead as a couple in their 30s, and two women in their 40s and 50s respectively.

Sgt. Dave Walker said the victims were shot at close range, and the investigation is leading the police into the illegal drug trade.

"There is reason to believe that methamphetamine was being used and sold from this residence in the recent past," he said, adding that police had made several drug arrests at the home previously.