In what police believe is an inside job, two masked men have broken into a Panorama City cell phone shop twice in the past week, looking to steal cell phones and tablet computers.

In the first robbery on Nov. 21, the men got away with a duffel bag holding 59 iPhones and 14 tablets, worth almost $52,000, Los Angeles police said.

The second time, Monday morning, a security guard surprised them as they left and they dropped the duffel bag.

Lt. Paul Vernon said detectives suspect the burglars either work at the store or know someone who does. They apparently made copies of keys to a safe holding electronics, and they knew the alarm code.

The thieves twice broke through a roof and slid down a rope into the Sprint Nextel store at 8500 Van Nuys Boulevard.

Police released store video of the first break-in, which can be viewed at http://tinyurl.com/duffelbagbandits.

Anyone with information should call Detective William Cooper at 818-838-9866. People also can call the LAPD tipline at 877-LAPD-247 (527-3247). Those who want to remain anonymous can call Crime Stoppers at 800-222-TIPS (8477) or text the organization by sending "LAPD" followed by a message to CRIMES (274637).