Grainy images reportedly taken on a cellphone Thursday, and shown on al-Jazeera and al-Arabiya, depict a bloodied Gadhafi struggling with his apparent captors in his hometown of Sirte.
He was then shown pushed onto the hood of a truck. Later images showed Gadhafi, with blood streaming down his face, staring lifelessly.
Stratfor, a private intelligence company in Texas, said one account of Thursday's events indicates NATO forces attacked a 100-car convoy thought to be carrying Gadhafi toward Misurata. A second account, offered by the interim government, said Gadhafi was captured in a drainage pipe by rebel fighters in Sirte.
U.N. Secretary-General Ban Ki-moon said Gadhafi's death "marks a historic transition for Libya."
"Yet let us recognize, immediately, that this is only the end of the beginning," he said. "The road ahead for Libya and its people will be difficult and full of challenges."
The U.N. Security Council in March authorized member states to "take all necessary measures" to protect civilians from attacks by forces loyal to Gadhafi. The International Criminal Court later issued an arrest warrant for Gadhafi for crimes committed since February.
U.S. Secretary of State Hillary Clinton told CNN that transitional leaders were waiting for Sirte to fall before declaring their country liberated.
"They knew if (Gadhafi) was at large, they would have continued security problems," she said. Clinton was in Tripoli just days before Gadhafi's death.
Stratfor adds that Gadhafi's death and the fall of Sirte are significant for a free Libya's future. It warned, however, the presence of multiple armed groups in the country and concerns mounting over the status of Libya's weapons present "serious implications for the future" of Libya.
NATO, in a briefing Wednesday, warned that the looting of weapons gave rebels the firepower they needed to oust Gadhafi but a highly armed population "is a problem that will need to be addressed quickly if it is not to create security issues further down the line."