Grainy images from one year ago Friday reportedly taken on a cellphone depicted a bloodied Gadhafi struggling with his apparent captors in his hometown of Sirte following a NATO strike on his convoy.
He was then shown pushed onto the hood of a truck. Later images showed Gadhafi, with blood streaming down his face, staring lifelessly.
The rights organization, in a 50-page report published Wednesday, said witness and video evidence suggests at least 66 members of Gadhafi's convoy were executed at a hotel in Sirte. Gadhafi's son, Mutassim, was allegedly taken by rebel forces from Sirte to Misuruta where he was killed.
Peter Bouckaert, emergencies director from the rights group, said the evidence collected suggests Gadhafi wasn't killed in a cross-fire, as alleged by interim authorities.
"The exact circumstances of his death remain unclear," the report reads. "Some militia fighters from Benghazi claim to have shot Gadhafi dead during a dispute with Misurata fighters about where to take him, but their claims remain unconfirmed."
The organization reminds Tripoli of its obligation to investigate alleged war crimes surrounding Gadhafi's demise.
"One of Libya's greatest challenges is to bring its well-armed militias under control and end their abuses," said Bouckaert from Beirut. "A good first step would be to investigate the mass executions of October 20, 2011, the most serious abuse by opposition forces documented so far."