A Rolling Hills Estates man told detectives Thursday he was responsible for burglarizing more than 100 cars in Manhattan Beach during the past six months, saying it was easy because “every car is unlocked,” police said.

Shawn Harriett admitted his crimes shortly after he was found sleeping in his blue Nissan Xterra parked on a Manhattan Beach street. Tuesday was his 24th birthday.

“He said he didn’t ‘break’ into any of them,” Manhattan Beach police Sgt. Paul Ford said. “He said all of them were unlocked.”

Harriett’s 7 a.m. arrest came about two hours after someone called police to report a vehicle burglary in the 700 block of 35th Street. A thief had entered the car and taken $300 in gift cards, $700 in scrip, or fundraising vouchers, from American Martyrs Church and cash.

Police officers could not locate a burglar, but received a call about 35 minutes later of a skateboarder trying to open car doors in the 700 block of 13th Street. He was last seen riding toward American Martyrs School, but officers were unable to find him.

After discovering Harriett slumped over in his driver’s seat at 15th Street and Harkness Avenue, police officers found a stolen driver’s license, American Martyrs scrip and gift cards, along with drugs.

Harriett also had used a stolen credit card Thursday at a nearby Walgreens, police said.

During questioning at the police station, Harriett admitted he had committed the morning crimes, along with stealing items from a vehicle in November and from a vehicle in Hermosa Beach in October, police said.

“Harriett stated he had entered ‘over 100 cars in Manhattan Beach over the past six months’ and when asked why he came to Manhattan Beach, he said, ‘You can come up in the beach cities, especially Manhattan Beach, (and) every car is unlocked,’ ” a police report said.

Harriett was arrested on suspicion of possession of stolen property, burglary, fraud, possession of narcotics paraphernalia and possession of narcotics. He was held at the Manhattan Beach jail on $20,000 bail.

Los Angeles County Superior Court records show Harriett has been arrested or convicted since 2010 of possession of marijuana while driving, possession of a controlled substance, grand theft, possession of methamphetamine, and receiving stolen property.

Police in Manhattan Beach, El Segundo, Redondo Beach, and the Los Angeles Police Department’s Harbor and Pacific areas have for years regularly issued warnings to residents about increases in thefts from vehicles, primarily because drivers do not lock their cars. The crimes have increased for years across the South Bay and Harbor Area.

“We definitely want people to know this is the reason people are coming here,” Ford said. “This is our third person that has actually mentioned that. Three different guys that don’t know each other. People in Manhattan Beach leave their cars unlocked.”

Manhattan Beach police officers specifically discussed locking vehicles during a town hall meeting on crime prevention Wednesday evening. About 250 people attended.

“You’ve got to lock your stuff up. You’ve got to secure your property. That’s what we’re trying to tell people in the South Bay,” Manhattan Beach police Officer Stephanie Martin said. “This just goes to it. This guy has been killing our community, getting stuff for free very easily. His statements summed it up.”