They're asking anyone who may know him as a friend, neighbor, or acquaintance to contact the sheriff's office as they try to figure out more about his past.
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Investigators say he lured the men to a remote section of Skyline Boulevard in San Mateo County on two separate nights last month.
Earlier this week, the suspect was in court for a hearing.
The judge reviewed his medical records and noted he was laughing randomly in court.
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All criminal proceedings are on hold until doctors can examine him.
A hearing is set for August 30 to hear the results of the evaluations.