The FBI accused Billy Lulo, 47, of mail fraud in connection with the theft of diamonds valued at $500,000 to $1 million in El Paso, Texas, the Los Angeles Times reported Wednesday.
Lulo's arrest came after a 10-month investigation, authorities said.
The sheriff's department hired Lulo in 1990. He was a level-one reserve assigned to patrol duties, a department spokesman said.
He was relieved of duty in November.