BEIJING -- A former chief librarian at a Chinese university admitted in court Tuesday to stealing more than 140 paintings by grandmasters in a gallery under his watch and replacing them with fakes he painted himself.

For two years up until 2006, Xiao Yuan substituted famous works including landscapes and calligraphies in a gallery within the library of the Guangzhou Academy of Fine Arts.

He told the court in his defense that the practice appeared to be rampant and the handling of such paintings was not secure. He said he noticed fakes already hanging in the gallery on his first day on the job. Later, after he replaced some of the remaining masters with his own fakes, he was surprised when he noticed his fake paintings were being substituted with even more fakes.

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"I realized someone else had replaced my paintings with their own because I could clearly discern that their works were terribly bad," Xiao, 57, told Guangzhou People's Intermediate Court, which posted a video of the two-hour hearing on its website.

Xiao said that he didn't know who had replaced his fakes, but that students and professors could take out paintings in the same way as they could borrow library books.

Xiao sold 125 of the paintings at auction between 2004 and 2011 for more than 34 million yuan ($6 million), and used the money to buy apartments and other paintings. The 18 others he stole are estimated to be worth more than 70 million yuan ($11 million), according to prosecutors.

Xiao pleaded guilty to a corruption charge for substituting the 143 paintings, and said that he deeply regretted his crime.

The stolen works mentioned in the court transcript included paintings by influential 20th century artists Qi Baishi, who used watercolors, and Zhang Daqian, who depicted landscapes and lotuses. Zhang himself was considered a master forger.

Also removed was "Rock and Birds" by Zhu Da, a painter and calligrapher who lived during the 17th century and used ink monochrome.

Xiao said he stopped his stealing when the paintings were moved to another gallery. He was the university's chief librarian until 2010, and his crimes came to light when an employee discovered what had happened and went to the police.

Calls seeking comment from the university were not answered.

Xiao will be sentenced later.