Retired army Maj. Santiago Martin Rivas, former leader of the "Colina" death squad, was cornered by police in a Lima apartment after detectives verified his identity during a week of surveillance, Interior Minister Gino Costa said.

Last year, a judge issued detention orders for Martin Rivas and 10 members of the Colina group for questioning in the still unsolved 1991 murders of 15 people in Lima's squalid Barrios Altos district.

Rivas and his former band are suspected of carrying out the killings, in which assailants used submachine guns fitted with silencers to raid a cookout in a tenement building.

The men were shielded from prosecution under a 1995 amnesty law signed by Fujimori. The law was also used to release them from prison following their 1994 convictions for killing nine students and a professor at La Cantuta University in 1992.

Costa said six other men from the Colina group have been arrested this year and that agents are searching for others tied to the group. He would not say how many suspects remain at large.

Both slayings were believed to be intended strikes at sympathizers of the now nearly defunct Maoist Shining Path guerrilla movement.

Tipped off by media reports of Martin Rivas' arrest, relatives of the Cantuta victims, carrying signs with pictures of the murdered students, demonstrated outside the apartment building where police held him before taking him into custody.

For years, human rights groups have suspected that Fujimori's ex-spy chief, Vladimiro Montesinos, masterminded the Barrios Altos and Cantuta killings.

Prosecutors reopened the cases in late 2000 to see if any direct link could be made to Montesinos, who is in jail facing more than 70 criminal charges, from influence peddling to drug trafficking.

The Inter-American Court of Human Rights, the legal arm of the Organization of American States, ruled last year that Peru's government bore responsibility for violating the rights of the Barrios Altos victims.

The Costa Rican-based court also said the 1995 amnesty laws passed to protect security forces from prosecution for human rights abuses lacked legal standing because they violated the American Convention on Human Rights, which Peru has signed.

Peru formally returned to the binding jurisdiction of the human rights court last year, two years after Fujimori refused to recognize its rulings in a dispute over secret military trials for four Chileans accused of involvement with Peruvian guerrillas.

Fujimori's 10-year autocratic regime collapsed in November 2000 when he fled to Japan amid bribery scandal involving Montesinos