The United Nations envoy to Libya has condemned the torture and killing of 12 people after their release from a militia-run prison.

The 12 were tried on charges of killing protesters during the 2011 uprising against Moammar Gadhafi. Justice Ministry spokesman Wessam al-Saghir says they were released Wednesday, but on the following day their bodies were found in different parts of the capital, Tripoli. The bodies had bullet wounds in their heads and bore signs of torture.

U.N. envoy Martin Kobler said Monday he was "utterly shocked and saddened by this heinous and vile crime."

Libya slid into chaos after Gadhafi was overthrown and killed, with an array of militias taking over much of the country. The killings illustrate the lingering lawlessness despite the formation of a U.N.-brokered unity government.