WASHINGTON (AP) — Secretary of State John Kerry says the Obama administration is making progress in its effort to hold people accountable for the Sept. 11 assault on a U.S. diplomatic installation in Benghazi, Libya.

Testifying before Congress, Kerry says the U.S. has identified people it believes were culpable in the attack that killed U.S. Ambassador Chris Stevens and three other Americans.

He says U.S. authorities are working through the evidence and making a case. This takes time, he says, because Libya remains largely lawless a year-and-a-half after the United States helped rebels there overthrow dictator Moammar Gadhafi.

The Obama administration has long promised to bring the perpetrators of the attack to justice.

Kerry didn't say if any suspect has yet been arrested, detained or otherwise targeted by American or Libyan authorities.