The former head of interrogations at Guantánamo Bay found that records of an al-Qaida suspect tortured at the prison camp were mysteriously lost by the US military, according to a new book by one of Britain's top human rights lawyers.

Retired general Michael Dunlavey, who supervised Guantánamo for eight months in 2002, tried to locate records on Mohammed al-Qahtani, accused by the US of plotting the 9/11 attacks, but found they had disappeared.

The records on al-Qahtani, who was interrogated for 48 days - "were backed up ... after I left, there was a snafu and all was lost", Dunlavey told Philippe Sands QC, who reports the conversation in his book Torture Team, previewed last week by the Guardian. Snafu stands for Situation Normal: All Fucked Up.

Saudi-born al-Qahtani was sexually taunted, forced to perform dog tricks and given enemas at Guantánamo.

The CIA admitted last year that it destroyed videotapes of al-Qaida suspects being interrogated at a secret "black site" in Thailand. No proof has so far emerged that tapes of interrogations at Guantánamo were destroyed, but Sands' report suggests the US may have also buried politically sensitive proof relating to abuse by interrogators at the prison camp.

Other new evidence has also emerged in the last month that raises questions about destroyed tapes at Guantánamo.

Cameras that run 24 hours a day at the prison were set to automatically record over their contents, the US military admitted in court papers. It is unclear how much, if any, prisoner mistreatment was on the taped-over video, but the military admitted that the automatic erasure "likely destroyed" potential evidence in at least one prisoner's case.

The erased tapes may have violated a 2005 court order to preserve "all evidence [of] the torture, mistreatment and abuse of detainees" at Guantánamo. The order was retroactive, so it also applies to the 2003 loss of al-Qahtani's records.

Lawyers representing other Guantánamo detainees are asking whether tapes of their clients' treatment may also be erased. "You can't just destroy relevant evidence," said Jonathan Hafetz, of the Brennan Centre for Justice in New York.

David H Remes, a lawyer for 16 Guantánamo prisoners, said the CIA's destruction of interrogation videos shows the US government is capable of getting rid of potentially incriminating evidence.

"[In Guantánamo] the government had a system that automatically overwrote records," Remes told the Guardian. "That is a passive form of evidence destruction. If a party has destroyed evidence in one place, there's no reason to assume it has preserved evidence in another place."

More than 24,000 interrogations were videotaped at Guantánamo, according to a US army report unearthed by researchers at Seton Hall University in New Jersey.

The US military office at Guantánamo did not return a request for comment from the Guardian about its taping policies.