David Willis reports from Kuala Lumpur: Anwar supporters want whoever administered the beatings to be prosecuted

Inspector-General of Police Abdul Rahim Noor said he assumed "full responsibility" and would resign effective from Friday.

But Mr Anwar's supporters say the resignation does not go far enough.

The police chief insisted Anwar was "safe and sound"

A legal adviser to Mr Anwar, Sivarasa Rasiya, told the BBC the resignation does not answer the question of who actually carried out the beating. His comments were echoed by opposition leaders and human rights groups.

Just days after Mr Anwar's arrest the police chief gave assurances that the former deputy premier was "safe and sound" in custody.

The dramatic resignation followed a long-awaited report from Malaysia's attorney-general on Tuesday which confirmed that police had injured Mr Anwar after he was arrested on charges of sex and corruption.

The report said a police investigation had failed to identify the person or persons responsible for the injuries.

The announcement came shortly after Prime Minister Mahathir Mohammad indicated he was considering setting up an inquiry into the beating Mr Anwar received on the night of his arrest on 20 September.

The prime minister has been under growing pressure from opposition politicians and the Malaysian Bar Council to find those responsible for the assault.

Dr Mahathir had earlier suggested that Mr Anwar may have inflicted the injuries upon himself.

DNA witness cross examined

Earlier in the day, with Mr Anwar's sex and corruption trial now in its third month, defence lawyers had been questioning the state's forensic expert and seeking to discredit his evidence.

Last week, Dr Lim Kong Boon testified that semen stains on a mattress seized from a smart apartment block matched Mr Anwar's DNA and linked him to a variety of sexual trysts with both men and women.

David Willis in Kuala Lumpur: Unlikely the resignation will mean an end to the controversy

But under cross-examination, Dr Lim admitted it was impossible to prove that the semen stains he examined were on the mattress before it was seized by the police.

The defence had previously implied that the police may have extracted semen from Mr Anwar after he was beaten unconscious on the night of his arrest.

Dr Lim's evidence is key to the prosecution's case, and having flown in DNA experts from Britain and Australia to assist them Mr Anwar's defence team was keen to undermine his credibility.

Questions of credibility

Defence lawyer Raja Aziz Addruse: It is not possible to determine the age of the stains

Had he ever worked with experienced pathologists, geneticists or forensic experts, asked defence counsel Raja Aziz Addruse?

"No," said Dr Lim.

Had any of his research been published in any scientific journals? Again, "No," the doctor replied.

The lawyer then tested him on a term which he said was well known amongst people in the field: what was the "stochastic effect?" Dr Lim said he had come across the phrase but could not remember its exact meaning, prompting laughter from the public gallery.

Samples destroyed

The mattress made another appearence in court

Mr Raja Aziz then asked whether the slides, containing semen samples taken from the mattress could be examined by the defence.

"They've been destroyed," replied Dr Lim, causing gasps around the courtroom. "It was not our practice to preserve such slides."

Mr Anwar's lawyers are seeking to prove that the former deputy premier is the victim of a political conspiracy aimed at destroying his career.