A search of the area concluded early Thursday without finding a suspect, said Deputy Morgan Arteaga, a department spokeswoman. A person detained during the search was not related to the case, she said.
The search had focused on a nearby building complex that provides housing to people with mental health issues.
A rifle-like pellet gun was found in one apartment and will undergo a forensic examination to determine whether it might have been used in the shooting, sheriff's officials said.
The victim, Deputy Angel Reinosa was treated and released following the Wednesday afternoon shooting, Arteaga said.
Reinosa, 21, was hit while heading to his car in the employee parking lot of the Lancaster station shortly before 3 p.m., Capt. Todd Weber said.
Mayor R. Rex Parris said the deputy was wearing a ballistic vest that deflected the bullet into his shoulder.
A Sheriff's Department statement Thursday said the round hit the top of Reinosa's right shoulder, damaging his uniform shirt but failing to penetrate his flesh. He was treated for the minor injury.
Deputies searched for the sniper inside the block-long, four-story structure with many windows that overlook the sheriff's facility in downtown Lancaster, a desert city of about 160,000 people north of Los Angeles.
"Apartment units were searched and multiple interviews were conducted" but no suspect was located, the statement said.
"Investigators believe this was an isolated incident targeting a deputy," the statement said.
Reinosa has been with the Sheriff's Department for about a year and joined the Lancaster station in May for patrol training, Weber said.
The apartment building is adjacent to and partners with a nonprofit that provides housing, counseling and other services to people with mental health issues, according to the website for Mental Health America, Antelope Valley Enrichment Services.
The nonprofit said several housing units are "designated specifically for individuals with disabilities ... who are ready for independent living."
But the mayor said the building "caters to, is designed for and allows mentally ill people to live there. That's all that lives there, is mentally ill people."
The sheriff's station is surrounded by shops and restaurants in a downtown area of the city in the Mojave Desert about 60 miles (100 kilometers) north of downtown Los Angeles.
Associated Press writer Robert Jablon in Los Angeles contributed.
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