The suspect in Sunday's mass shooting at a Fayette County car wash has been pronounced dead.

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Timothy O'Brien Smith, 28, was pronounced deceased by two separate doctors at Forbes Regional Hospital at 8:54 p.m. Sunday, Pennsylvania State Police said Tuesday.

Smith was accused of shooting and killing four people early Sunday morning at a car wash in Melcroft, located about 55 miles southeast of Pittsburgh. Investigators believe he then turned the gun on himself.

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The victims -- identified as William Porterfield, 27; Chelsie Cline, 25; Courtney Snyder, 23; and Seth Cline, 21 -- were pronounced dead at the scene. There was a fifth person with the victims that night who managed to escape with minor injuries.

Chelsie Cline used to date Smith, family members said.

The motive behind the shooting remains unclear.