The AP news agency quoted Mustafa Abdul-Jalil as saying that an NTC team will investigate the killing amid conflicting reports of how Qaddafi died.
Abdul-Jalil suggested that Qaddafi could have been killed by his own supporters to prevent him from implicating them in past misdeeds under his regime.
Libya's new authorities had said initial findings suggest Qaddafi was killed in the crossfire as his supporters clashed with revolutionary forces seizing control of Sirte.
The United States, Britain and human rights groups have called for an inquiry into whether rebels killed a wounded Qaddafi after capturing him.
NTC Urged To Investigate Qaddafi Supporters' 'Execution'
In related news, a human rights group has called on the new Libyan authorities to investigate the suspected mass execution of dozens of supporters of Muammar Qaddafi and urged a crack down on crimes by anti-Qaddafi fighters.
The New York-based Human Rights Watch (HRW) organization said 53 bodies were found last week in Qaddafi's hometown of Sirte, surrounded by spent cartridges.
HRW officials who saw the bodies said some of the victims had their hands tied behind their backs when they were shot and were identified by local residents as Qaddafi loyalists.
The group called on the National Transitional Council (NTC), Libya's new leadership, to conduct an "immediate and transparent" investigation into the deaths in Sirte.
HRW also said it had found the remains of at least 95 people at the site where Qaddafi was captured.
It said most of these had been killed in fighting and NATO strikes but between six and 10 appeared to have been executed at the site.
compiled from agency reports