US officials believe Wall Street Journal reporter Daniel Pearl was killed by alleged 11 September mastermind Khalid Sheikh Mohammed, reports say.
Mohammed is being held at an undisclosed location
The Journal reported on Tuesday that officials had information that Sheikh Mohammed was directly involved.
However some senior Pakistani officials have expressed doubt about such allegations.
Daniel Pearl was abducted and subsequently killed in 2002.
Sheikh Mohammed - a suspected top Bin Laden aide - was captured in Pakistan in March.
US officials have developed "credible, corroborated information" that it was Sheikh Mohammed who killed Mr Pearl, the Wall Street Journal said.
Previous reports from the region had suggested that Sheikh Mohammed was behind the journalist's murder.
"We didn't know one way or the other, our government has subsequently come to the conclusion that what they were saying was correct," a US official told Reuters news agency, without revealing what information had led them to this belief.
Four people have so far been convicted in connection with Pearl's murder
But senior Pakistani officials told the Associated Press that they could not confirm these suspicions.
"Many newspapers have been reporting it. We do not have evidence or credible information," the news agency quoted an unidentified official as saying.
Since his arrest in the Pakistani city of Rawalpindi this year, Sheikh Mohammed has been held at an undisclosed location and interrogated by CIA officials.
He is suspected of being the chief planner of the 2001 attacks on the World Trade Center and the Pentagon.
He is also accused of plotting to blow up several American airliners flying from south-east Asia to the United States in January, 1995.
However, three senior Pakistani officials involved in the Pearl case have told the Associated Press that they could not confirm the suspicions that Sheikh Mohammed was Daniel Pearl's killer.
An interior ministry official said that Pakistani investigators had questioned him about the Pearl case after he was arrested but he never acknowledged any role in the murder while he was in Pakistani custody.
Mr Pearl, the Wall Street Journal's South Asia bureau chief, disappeared in January 2002 while researching a story about Islamic extremists.
Photographs of the journalist in captivity were e-mailed to news organisations, along with demands for the release of al-Qaeda and Taleban suspects being held by the Americans.
Later, a gruesome videotape of Mr Pearl's murder was sent to US officials and his body was discovered the following May.
British-born Islamic militant Ahmed Omar Saeed Sheikh was convicted last year by a Pakistani court of involvement in Pearl's kidnapping and murder, and sentenced to death.
Three accomplices were given life imprisonment. All four are appealing against their sentences.
The Wall Street Journal says that among the many unresolved questions in the Pearl case, the most basic are: Who ordered him killed and why?