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Lima, Peru (CNN) -- Peruvian police said Thursday they found skin underneath the fingernails of a 21-year-old student Joran van der Sloot is accused of killing.

Miguel Canlla Ore, a colonel in the Peruvian National Police and head of homicide, told journalist Victoria Macchi that the amount of skin was small and that laboratory DNA tests that might indicate who it came from had not been completed.

Peruvian authorities have charged the 22-year-old Dutchman with murder in the death of Stephany Flores, whose body was found June 2 in a hotel room registered to van der Sloot.

He also is the lead suspect in the 2005 disappearance of Alabama teenager Natalee Holloway in Aruba.

Van der Sloot was arrested twice in connection with Holloway's disappearance but was never charged because of a lack of evidence.

A court document obtained by CNN shows Flores had a cranial fracture and other injuries to her face and neck and showed signs of asphyxiation. Forensic tests in the hotel room where her body was found showed blood on the floors, hallway and mattress, the document said.

According to transcripts of van der Sloot's confession, he said he elbowed Flores in the face before strangling her and then suffocating her with his shirt. The transcripts were provided to CNN by a police source who has not been named because he was not authorized to pass along the material.

Van der Sloot told authorities he attacked Flores on May 30 after she read an e-mail in his computer connected with the Holloway case. After killing Flores, police say, van der Sloot took money and bank cards from her wallet and fled to Chile, where he was arrested June 3.

He was returned the next day to Peru.

Van der Sloot is being held in a high-security area of the Miguel Castro Castro Prison, where only two of 10 cells are occupied and he has no contact with the general prison population.