El Salvador's human rights agency says the government has failed to properly investigate the 1975 killing of poet Roque Dalton, who was allegedly slain by leaders of a leftist guerrilla group in which he was a member.

The guerrilla group later joined the Farabundo Marti National Liberation front, the forerunner of the current FMLN political party that governs El Salvador.

Dalton was a political activist who joined the Revolutionary Army of the People. Reports at the time said he was killed by his own comrades because they suspected he might be an infiltrator or informant.

El Salvador's Prosecutor's Office for the Defense of Human Rights said in a report Tuesday that the government should investigate the group's leadership and also find Dalton's body.