Officers responded to a report of a shooting at Twinbridge Circle near Longbrook Way just before noon.
Witnesses reported hearing multiple gunshots with two victims injured and lying on the ground, officers said.
The victims were taken to John Muir Medical Center in Walnut Creek. Police said a 67-year-old man died at the hospital.
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Police said the identities of both victims are withheld pending contact with family members.
This is the second homicide of the year.
Police are looking for a male suspect. No arrests have been made.
Any person with information related to this crime is encouraged to contact the Pleasant Hill Police Investigations Bureau at (925) 288-4630.
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