As the rebel fighters battled their way deeper into Sirte on Oct. 20, Muatassim Gadhafi, in charge of the city’s defense, ordered his father’s inner circle and some remaining civilians to flee the area in a convoy of about 50 heavily armed vehicles, Human Rights Watch said.

“The escape attempt was doomed,” the report said.

The convoy was struck first by a NATO drone-fired missile, and then ran into the particularly fierce fighters from Misrata, which had suffered a merciless attack by regime forces and was eager for revenge. Airburst bombs rained down from a NATO warplane, which “incinerated dozens of Gadhafi fighters,” the report says.

The convoy’s survivors fought the militiamen while Gadhafi and some of his loyalists fled the scene, only to be captured as they tried to escape through drainage pipes underneath a major road nearby.

In a last-ditch effort to avoid capture, one of the leader’s bodyguards threw a hand grenade at the Misrata fighters, but it bounced back and exploded among Gadhafi’s circle, killing Defense Minister Abu Bakr Younis on the spot. Gadhafi and others received wounds from spraying shrapnel, the report says, but they were clearly alive upon capture.

Human Rights Watch said it remains unclear whether Gadhafi died from the rebels’ violence or the wounds he’d suffered in the ambush.

“Gadhafi was immediately set upon by the Misrata fighters, who wounded him with a bayonet in his buttocks, and then began pummeling him with kicks and blows,” Human Rights Watch said, citing witness interviews and cell-phone footage from the scene. “By the time Moammar Gadhafi was loaded into an ambulance and transported to Misrata, his body appeared lifeless.”

Gadhafi’s son met the same end, but projected defiance even in captivity. A video, which Human Rights Watch says was filmed by an associate of the Lions of the Valley militia, shows Mutassim reclining on a bed, being offered water and cigarettes.

When the captors reassure him they’ll treat his wounds, an apparent attempt to show moral superiority over a former ruler, Mutassim replies that the wounds “are my medals.” The detainee then lectures the captors for filming him and tells them to stop acting like adolescents, the report says.

His attitude enrages the militiamen, who threaten him: “You think this is child’s play? You’ll see when we are finished with you! You will see, you dog!”

Hours later, Mutassim Gadhafi was dead. Human Rights Watch viewed his body the next day, Oct. 21, and found “a large wound on his throat which did not exist in the video images of the captured Mutassim.” He also had a large gash on his lower stomach.

Human Rights Watch wasn’t allowed to turn the body over for a fuller inspection, and the government has so far refused to release the results of autopsies conducted on Gadhafi and his son, despite repeated requests from the U.N.’s Commission of Inquiry for Libya.

There are no doubts, however, about the deaths of the dozens of regime loyalists whose rotting corpses were found in the nearby Mahari Hotel. A Human Rights Watch research team counted at least 53 dead, “some with their hands still bound behind their backs,” clustered together in the hotel’s sea-view garden. Relatives already had retrieved additional corpses, locals told the team.

Using morgue records, photo identification and other tools, Human Rights Watch was able to identify many of the decomposing bodies. They included Abdelaziz Ajaj Ahmayd, a 45-year-old nephew of Gadhafi’s. Video footage shows him being questioned, slapped and spat upon, the report notes. His body was buried at the hotel as unidentified body No. 97.

Another of the corpses belonged to Ahmed Ali Yusuf al Ghariyani, 29, a soldier originally from Tawergha, a community of dark-skinned Libyans whose village was razed by Misrata rebels, who accused the locals of collaborating with the regime. The video shows Ghariyani beaten, kicked and pelted with shoes as Misrata rebels taunt him about his roots. He was buried as body No. 86.

“Establishing responsibility for the apparent execution of at least 53 and perhaps as many as 66 persons at the Mahari Hotel will require further investigation,” Human Rights Watch said. However, the report added, “it is likely that a large number of Misrata-based militiamen were involved in, and have knowledge of, the apparent executions at the Mahari Hotel.”