Peru's attorney general has asked Congress to pursue homicide charges against former President Alberto Fujimori in connection to a 1991 massacre, local media reported Thursday.

Nelly Calderon filed a "constitutional denunciation" against Fujimori late Wednesday in connection with 15 deaths in a tenement building in Lima's Barrios Altos district, allegedly committed by the Colina death squad, radio and television reports said.

Human rights groups say the squad was formed by fugitive former spy chief Vladimiro Montesinos to combat rising attacks by Maoist Shining Path guerrillas. The November 1991 killings were carried out with submachine guns fitted with silencers.

Fujimori allegedly went to the National Intelligence Service headquarters "to celebrate" with the perpetrators on the day of the massacre, newspaper El Comercio reported Thursday.

Calderon's report to Congress cited testimony from three former members of the group, who claimed Fujimori knew about their actions.

Calderon alleged that Fujimori could have issued orders through Montesinos, who dealt directly with the squad's chief, retired Maj. Santiago Martin Rivas.

El Comercio reported that on July 30, 1991 -- four months before the killings -- Fujimori signed a memorandum recognizing the Colina squad for its "successful intelligence operations," and authorized an unspecified "incentive" to key members.

As a former president, Fujimori has constitutional immunity from prosecution. A congressional subcommittee is already investigating allegations of Fujimori's alleged involvement with the group and must pass its findings to the legislature for a vote before Calderon can pursue charges in court.

A similar process was used earlier this year to charge Fujimori with abandonment of office and dereliction of duty.

Fujimori's 10-year autocratic rule ended in November after he fled to Japan, his parents' homeland, amid mounting corruption scandals surrounding Montesinos. Fujimori has denied any criminal wrongdoing.

Calderon also alleged that Fujimori protected the group from prosecution, pushing through a 1995 military and police amnesty used to secure their release from prison for the 1992 assassinations of nine students and a professor at La Cantuta University.

The Barrios Altos case was reopened in March after a ruling by the Inter-American Court of Human Rights, the legal arm of the Organization of American States, to investigate and punish those responsible.