Customers reportedly called 911 at 2:15 a.m. Monday when they entered the McDonald's drive-thru and didn't receive a response, but noticed the lights were on and the back door was open.

San Diego police responded to the call but found no one inside the restaurant located at Mission Gorge Road and Ranier Street.

The manager said the restaurant was closed at the time but did not offer an explanation as to why the door was left open, according to police.