The UN resolution that was agreed upon on Saturday called for the International Criminal Court to investigate the killings.
However, it has been widely reported that Gaddafi hired foreign mercenaries to carry out some of the killings. The US insisted that the resolution was worded in such a way that no one from a country that is not a member of the ICC can be prosecuted. Meaning that mercenaries from countries that are not ICC members cannot be prosecuted for any crimes they may have committed in Libya. (Please note we don’t know exactly from which countries they came. Some countries that have been named are ICC members, while others are not)
It is believed that the US pushed for this move in order to prevent setting a precedent of prosecuting criminals from non-ICC members, presumably to prevent Americans from being prosecuted for crimes committed elsewhere.
The US was once an ICC member, but withdrew under President George W. Bush in 2002, who declared the ICC had no power over Washington.
Read the article here