DENVER, Colo. -- A library patron suspected of selling hundreds of books, tapes and DVDs he had borrowed has cost Denver-area libraries tens of thousands of dollars, library officials said.

Thomas Pilaar, 33, was suspected of using different names to obtain seven library cards from the Denver Public Library, then checking out 300 items per card and selling at least some of the items, according to reports.

"It appears his intent was to sell 2,100 (items) from the Denver Library collection," Denver Public Library spokeswoman M. Celeste Jackson told said. She estimated the losses at about $35,000.

Arapahoe County library administrators told a reporter that Pilaar obtained three library cards and checked out between 250 and 300 items.

James Larue, Douglas County's head librarian, said Pilaar checked out more than 300 items from two county libraries and had $11,000 worth of overdue items.

Authorities were tipped by a woman who recently bought books through the online classified ad site Craigslist.org and noticed the library identification stamps.

Pilaar was jailed on an unrelated parole violation and was being investigated for theft, said Lynn Kimbrough, spokeswoman for the Denver District Attorney's Office. He was being held without bond.

Pilaar declined a request seeking comment.

The Denver Public Library is reviewing its policy on allowing patrons to borrow up to 300 items at a time.