ISLAMABAD, Pakistan — The top Qaeda operative accused of masterminding the September 11, 2001, attacks either killed or took part in the murder of Wall Street Journal reporter Daniel Pearl, Pakistan’s president has alleged for the first time.

President Musharraf’s claim, made in his memoirs released this week, could now be used to try to clear one of Pearl’s four convicted killers, who is appealing his death sentence, the prisoner’s lawyer said yesterday.

General Musharraf accused Khalid Sheikh Mohammed of taking part in Pearl’s killing in Pakistan’s largest city, Karachi, following the journalist’s kidnapping on January 23, 2002. Mr. Mohammed was arrested in Pakistan in 2003 and is in American custody in Guantanamo Bay, Cuba.

“The man who may have actually killed Pearl or at least participated in his butchery, we eventually discovered, was none other than Khalid Sheikh Mohammed, Al Qaeda’s no. 3,” General Musharraf wrote in “In The Line of Fire,” released Monday.

Mr. Mohammed has never been officially linked to Pearl’s murder during police investigations or the trial that resulted in four Islamic militants being convicted for the killing. One of the men was sentenced to death, and the other three to life in prison.

But some American officials and the Wall Street Journal suggested that Mr. Mohammed had killed Pearl. Pakistan denied the claims at the time.

General Musharraf also wrote that Mr. Mohammed helped lay the groundwork for the London subway bombings on July 7, 2005, and a plot to attack Heathrow Airport with hijacked passenger planes. It was the first public allegation linking Mr. Mohammed to the subway attacks, which killed 52 people and four bombers.

The head of terrorism research at Singapore’s Institute of Defense and Strategic Studies, Rohan Gunaratna, said it has long been understood that it was Mr. Mohammed who killed Pearl to prove to the West after September 11 that Al Qaeda was still bent on killing Americans.

“But Pakistan never officially acknowledged it because they did not want to risk letting the others in custody be released,” Mr. Gunaratna told the Associated Press.

Yesterday, a lawyer for British-born Pakistani Ahmed Omar Saeed Sheikh, Rai Bashir, said he would petition the Sindh High Court in Karachi within 10 days to let him introduce General Musharraf’s book as evidence in his client’s appeal, which began in January 2003.

Mr. Sheikh and three other Islamic militants were convicted in July 2002 of killing Pearl. All have since appealed.

Mr. Bashir said he will try to use General Musharraf’s book to highlight contradictions in the prosecution’s case against Mr. Sheikh, who has been sentenced to death. He declined to elaborate.

It was unclear if American authorities would bring charges against Mr. Mohammed over Pearl’s killing. A representative for Pearl’s family declined to comment.

In Washington, a State Department spokesman, Sean McCormack, said the American government had evidence relating to General Musharraf’s assertion.

“We believe that it would be better and more appropriate to offer such evidence in the context of a military tribunal,” Mr. McCormack said. “We hope, as the U.S. government, that once we do get legislation that governs those military tribunals, that we can be in a position to offer up evidence related to that [General Musharraf’s] assertion.”

The Bush administration and the Congress are working on new procedures to interrogate suspects in the war on terrorism following a U.S. Supreme Court ruling striking down the previous system of military trials.

Mr. Bashir said General Musharraf referred to two men never charged in the Pearl killing — Mr. Mohammed and another detained militant suspect, Fazal Karim.

General Musharraf alleged in his memoir that Mr. Mohammed, a joint Pakistani-Kuwaiti citizen, confessed after being captured to participating in Pearl’s killing.

General Musharraf also recounted the May 2002 arrest of Karim, an activist from the Qaeda-linked Lashkare-Jhangvi group, who led investigators to Pearl’s body and confessed to being involved in his killing.

General Musharraf wrote that police had asked how Mr. Karim knew where Pearl’s body was buried.

“Chillingly, he replied — without remorse — that he knew because he had actually participated in the slaughter by holding one of Pearl’s legs,” General Musharraf wrote.

But Mr. Karim told police that he did not know the name of Pearl’s actual killer, only that he was “Arab-looking.”

At the time, police identified Mr. Karim as one of the men who located Pearl’s body. However, the police officially refused to confirm details and never charged him in the murder.

Mr. Karim disappeared shortly after leading investigators to Pearl’s shallow grave. In April 2003, he surfaced in a small-town jail charged with possessing outlawed drugs. His current whereabouts are unknown.

Mr. Karim’s lawyer, Khawaja Naveed Ahmed, questioned why his client was not charged in Pearl’s murder despite “incriminating evidence” disclosed in General Musharraf’s book.

General Musharraf detailed in his book how Mr. Sheikh plotted to kidnap Pearl, who was in Pakistan researching a story on Islamic militancy, by making the journalist believe he had arranged an interview with a militant leader in Karachi.

Pearl was kidnapped the day he arrived in Karachi, and his remains were found February 21, 2002.