RENO — Prosecutors are investigating whether an off-duty Reno police officer found passed out in his car last month was drunk and why responding officers waited to get help from another police agency.

The patrol officer, Chad Johnston, 33, was convicted last year of driving under the influence after breath tests showed he had more than twice the legal limit of alcohol in his system, according to court documents.

In the latest case on Feb. 14, two hours passed between the time a woman reported seeing an unconscious man in his car in the Silver Legacy hotel-casino parking garage and the time that a Washoe County sheriff's deputy performed a field sobriety test on Johnston.

Johnston passed the test, but the sheriff's office questioned the way the incident was handled by Reno police and asked prosecutors to investigate whether charges should be filed, said Brooke Keast, a sheriff's spokeswoman.

"There are things that happened with this case that need to be explained, and I am seeking answers," Assistant District Attorney John Helzer told the Reno Gazette-Journal. "There are some substantial portions of this case that need to be investigated."

Because the case involved a colleague, Reno police initially called the Nevada Highway Patrol for assistance, then the sheriff's office.

After the February incident, Johnston was taken off his patrol job and given administrative duties while the case is reviewed, said Reno police spokesman Steve Frady.

Frady said he could not comment on the timeline or circumstances surrounding the case because the department had not seen the report.