Police have arrested a man suspected of breaking into 50 cars to steal drivers' licenses and vehicle registration cards so he could ransom them back to their owners, Qingpu district police said Wednesday.

After each break-in, the suspect, surnamed Wang, would typically leave a note with his cell phone number demanding money in return for the documents, according to a police press release.

"Wang usually asked the car owner for 200 yuan ($32.50) to 300 yuan," said Jin Bin, a press officer with the Qingpu District Public Security Bureau. "Some owners just paid the money because the amount wasn't very much and it saved them the trouble of applying for new licenses and registration cards."

Wang usually wouldn't take the documents with him. Rather, he would hide them in the car under the seats or within crevasses in the interior. Sometimes, he would steal other valuables he found in the cars, Jin said.

Wang had worked at an auto repair shop and used specialized tools to open the cars' windows, according to the press release. He once managed to break into six cars in one night.

Police said Wang admitted to breaking into vehicles in Qingpu, Songjiang, Minhang and Jiading districts, according to the press release.

Qingpu district police first received a report about the break-ins on April 27, when a car owner reported someone had stolen his driver's license and vehicle registration from his car.

Jin said that many drivers incorrectly assumed that replacing their drivers' licenses and vehicle registration cards would require a lot of time and effort, but most people can obtain new documents the same day they report them lost.

Police suggested car owners should report such thefts to police and search their vehicles thoroughly to see if the documents are hidden inside.

Police are still investigating the case.