The family of Daniel Pearl has expressed skepticism over a claim by the alleged mastermind of the 9/11 attacks, Khalid Sheikh Muhammad, that he personally beheaded the American journalist five years ago. Muhammad, who claimed responsibility for a spate of terrorist attacks on behalf of al-Qaida, told a US military hearing at Guantanamo Bay that he had executed Pearl for allegedly being an Israeli agent, according to a transcript released by the Pentagon last week. "I decapitated with my blessed right hand the head of the American Jew, Daniel Pearl, in the city of Karachi, Pakistan," Muhammad said. "For those who would like to confirm, there are pictures of me on the Internet holding his head." Pearl's murderers filmed his death, and video released on the Internet shows a man holding the reporter's head, but the man's face is blacked out. Muhammad was quoted as saying he first suspected that Pearl - a Wall Street Journal reporter researching an article about Islamic extremists - had been a CIA agent. But he later said that al-Qaida came to believe the son of an Israeli professor was instead working for the Mossad. Pearl's parents, Ruth and Judea Pearl, said in a statement from their home in Encino, California, that they were treating Muhammad's statement cautiously. "It is impossible to know at this point whether Khalid Sheikh Muhammad's boast about killing our son has any bearing in truth," they said in a statement e-mailed to The Jerusalem Post. "We prefer to focus our energy on continuing Danny's lifework through the programs of the Daniel Pearl Foundation which aim to eradicate the hatred that took his life." The foundation works to promote cross-cultural understanding, and last week announced its sponsorship of journalists Amr Emam from Egypt and Zaineb Obeid from Iraq to work for six months in US newsrooms. In an interview with ABC News, Pearl's father said many unanswered questions remain. "We don't know the identities and the whereabouts of the three Arabs who came the last day [of his captivity] and performed the murder," he said. While Muhammad claims to be one of them, Pearl said the facts "don't match his story." "He wants to take credit for doing it, and he wants to exonerate al-Qaida, blame Pakistan, and whatever," Pearl said. "When a person confesses, he has nothing to lose. You have to take it with a spice of doubt." Daniel Pearl's widow, Mariane, said she would not be intimidated by Muhammad's brand of terrorism. "The more people like Khalid Sheikh Muhammad spread fear, the more determined I am to resist by celebrating the values of humanism and dignity," she said in a statement. "The only way to fight terrorism is to exercise self-control over the natural feelings of disgust and horror that his declarations provoke." In Pakistan, Rai Bashir, a lawyer for Ahmed Omar Saeed Sheikh, who was sentenced to death in 2002 for murdering Pearl, said he would use Muhammad's testimony as evidence that his client was not guilty. "What we were saying for so many years in our trial, in the appeal, [is] that Ahmed Omar Saeed Sheikh is innocent and he has not committed that murder," Bashir told Associated Press Television News in an interview in the eastern city of Lahore on Saturday. "He has not abducted Daniel Pearl, and he, along with his co-accused, is innocent. But now we are happy that this version has been verified by the Pentagon after the arrest of Khalid Sheikh Muhammad." He did not say when he would officially file Muhammad's claim as evidence in the appeal. Pearl, 38, was abducted in January 2002 in Pakistan's largest city, Karachi, while he was researching a story on Islamic militancy. Months later his body was found with his throat slit in a shallow ditch on the city's outskirts. Later in 2002, a Karachi antiterrorism court sentenced the British-born Sheikh to death. It sentenced three other men - Salman Saqib, Fahad Naseem and Sheikh Adil - to life in prison for involvement in Pearl's murder. Bashir is representing all four men, who are in jail and have appealed their convictions. The High Court in the southern Sindh province, of which Karachi is the capital, is hearing the men's appeals. The proceedings have been delayed repeatedly, mainly due to requests by defense lawyers for more time. Muhammad was captured in March 2003 in Rawalpindi, a city near Pakistan's capital, Islamabad. US officials suspect Muhammad might have claimed responsibility for dozens of terrorist attacks since 1993 to spare some of his fellow detainees at Guantanamo Bay. They also said he might have exaggerated his own role in terrorist attacks for self-glorification, or to take the spotlight off others involved. Legal experts have cast serious doubt about the validity of his claims as evidence, saying they merely illuminate a "sham process" of justice in the US war on terror, including the alleged use of torture on Muhammad to extract a confession. The CIA denies Muhammad was tortured, but evidence to the contrary has been building for years. Brad Pitt and Angelina Jolie are working together on a film about Daniel Pearl and his wife, who was six months pregnant when he was murdered, called A Mighty Heart. It is due to be released later this year.