Philip Hammond, Defense Secretary, has said the death had “stained” the reputation of Libya’s fledgling interim government.
Mr Ghoga said: “With regards to Gaddafi, we do not wait for anybody to tell us.
“We had already launched an investigation. We have issued a code of ethics in handling of prisoners of war. I am sure that was an individual act and not an act of revolutionaries or the national army.”
Col Gaddafi was taken, bloodied, but alive, from the drain after his failed attempt to flee Sirte and mobile phone footage showed him being beaten and tortured as jubilant rebels surrounded him.
He died on his way to hospital of bullet wounds to his head and chest according to a post mortem.
Until now, the official NTC account has maintained that the dictator was killed in crossfire in fighting with loyalists after he was captured.
However conflicting rebel accounts and mobile phone footage have instead identified several different men as Col Gaddafi’s killer.
One piece of film taken soon after the killing shows an unnamed young fighter, brandishing a handgun, standing next to an ambulance bearing Col Gaddafi’s body and being lauded by his comrades.
Fighters from the city of Misurata were the first to find Col Gaddafi and few have shown any sympathy for his death. Doctors estimate the city suffered more than 1,500 killed after it rose against the Gaddafi regime.
Nasser Zintani, said: “If Gaddafi came back to life, I would kill him again a million times. Gaddafi was sentenced to death long ago and the man who did it was merely carrying out his sentence.”
Yassin Humaid, commander of the Shuhada Square brigade, said: “I am happy Gaddafi is dead, but if the way he was killed was against human rights and the Geneva Convention, then they should go to court. We are with the law.”
The UN voted to cancel its authorization for military action at the end of October 31 despite an NTC request that Nato continue operations until the end of the year to stop the loyalists escaping to neighboring countries.
William Hague, Foreign Secretary, said the decision was “another significant milestone towards a peaceful, democratic future for Libya”.
He said: “Ending the no-fly zone and the civilian protection provisions demonstrates that Libya has entered a new era.”
The NTC had “a duty to uphold human rights and must prevent reprisals and revenge attacks” after Col Gaddafi’s death, he added.
Meanwhile Abdullah al-Senussi, Col Gaddafi’s fugitive intelligence chief, had passed from Niger into Mali, security sources from both countries claimed.
Mr al-Senussi and Col Gaddafi’s son, Saif al-Islam, are both wanted by the International Criminal Court (ICC) for their role in the repression of the uprising.
An NTC source claimed Saif al-Islam had requested an aircraft to fly him from Libya’s southern desert to the Hague, where he intended to hand himself over to the ICC.