MISURATA, Libya — On the night that he was to die, Hassan Nahassi should have been safe.

It was Oct. 20. A middle-age man turned Libyan rebel commander, Mr. Nahassi had returned home in the evening, leaving behind the front lines of Surt for a reprieve from the fighting. He wanted to rest with his wife and children.

Then came the news. Muatassim el-Qaddafi, a son of Col. Muammar el-Qaddafi, had been captured on the front that Mr. Nahassi had left only hours before.

Muatassim was loathed and feared. Word of his capture sent elation coursing through his enemy’s ranks. Around Misurata, rebels began firing into the night sky, celebrating a milestone in the slow, inevitable dismembering of the Qaddafi clan.

At Mr. Nahassi’s home, Sadiq, his 14-year-old son, asked if he might fire a burst. “Please father,” the boy recalled asking. “I need the rifle, the Kalash.”