A gunman walked into an exercise class at a health club and opened fire, killing four people and himself and injuring at least 10 others.
"He did not say anything," Allegheny County police Superintendent Charles Moffatt said. "He walked right into the room where the shootings occurred as if he knew exactly where he was going."
The shooting happened last night at the LA Fitness Centre in Bridgeville, Pennsylvania, a community of about 5,000 not far from central Pittsburgh and Pittsburgh International Airport.
Debi Wozniak, of Dormont, a suburb of Pittsburgh, was running late and did not make it to her weekly Latin impact dance exercise class, but her sister Joann Gazzam, who was there, told her the man came in through glass double doors at the exercise room's entrance.
He walked to the back of the room near some weights and set down a bag, fumbling with it for a few minutes and came up with what Ms Gazzam said were apparently two guns and began shooting.
Ms Gazzam told her sister several people appeared to be wounded, including the instructor, and that it was apparent that four people were dead and that the gunman had killed himself.
UPMC Mercy Hospital said five critically injured women were taken there. Allegheny General Hospital said it had two women in a fair condition with gunshot wounds.
St Clair Hospital said one of the victims of the shooting died there. Spokesman Rich Sieber said the woman was shot in the chest.
He said two other victims were taken to his hospital, both in a stable condition.
The fitness centre, which opened last year, is in a strip mall called the Great Southern Shopping Centre, where a few businesses were destroyed in a 2006 fire.
It said in a statement: "Each of us in the LA Fitness family are shocked and saddened by the senseless acts of violence that took place."