A prominent human rights advocate last night told a Law School audience that a variety of problems prevent new democratic regimes from successfully prosecuting past human rights offenders.

Focusing on four South American nations, Chilean exile Jose Zalaquett said three legal obstacles make it difficult for democratic leaders to punish their predecessors for imprisoning, torturing, and murdering thousands of people.

Zalaquett, former deputy secretary general of Amnesty International, said the arbitrary detention of citizens is not always defined as illegal in Uruguay, Chile, Brazil, and Argentina.

Because law prevents plea-bargaining, officials have problems persuading the accused to confess to crimes and reveal information about other police, military, and government officers, he said.

In Argentina, prosecution efforts have been hindered further by a general amnesty declared by the outgoing military junta in 1982. The bill absolved perpetrators of human rights violations of their offenses.

Argentine President Raul Alfonsin annulled the amnesty in 1983, but it remains a subject of legal debate.

Zalaquett stressed that even if these technical problems can be overcome, the political climate may be unfavorable for the vigorous prosecution of past leaders.

Zalaquett was expelled from Chile in 1976 after serving time in prison because of his protests against the government's human rights violations. His lecture was the first of a series of events on human rights scheduled for this fall at the Law School.