(AP) Boris Weisfeiler was one of more than 3,000 people who vanished after being arrested during the military dictatorship of Gen. Augusto Pinochet. He's the only American still missing.

Yet his sister said Friday she holds out hope he is alive, 21 years later.

"I know he was alive two and a half years after his disappearance because there are some people who saw him; so if he was alive then, he may still be alive now," Olga Weisfeiler said at a news conference with U.S. Ambassador Craig Kelly.

Finding out what happened to Weisfeiler is a "high priority" for the American government, Kelly said.

A Russian-born naturalized U.S. citizen, Boris Weisfeiler was 43 when he was arrested by a military patrol while camping near Parral, 210 miles south of the capital Santiago in 1985. The Pennsylvania State University mathematics professor has been missing ever since.

U.S. Secretary of State Condoleezza Rice expressed concern about the Weisfeiler case earlier this month when she attended the inauguration of Chilean President Michelle Bachelet _ herself once a political prisoner under Pinochet.

More than 3,000 people disappeared or were killed for political reasons during Pinochet's 1973-90 rule, according to a report by an independent commission appointed by the government that succeeded the former dictator.

Weisfeiler was one of four American victims but only he remains missing; bodies of other three have been found, according to the commission.

But the circumstances behind the disappearance of Weisfeiler, who Chilean authorities and his sister say was in the country as a tourist, has remained a mystery.

Olga Weisfeiler, of Newton, Mass., said her brother "was not interested in politics at all" and was there only to hike and camp.

Weisfeiler said she would remain in Chile for a week to meet with the government, court officials and army commander Gen. Oscar Izurieta to ask for support. She also said she hoped new information would emerge from an investigation by Chilean authorities into Colonia Dignidad, a secretive German enclave where he was reportedly last seen.

Pinochet, now 90, is himself free on bail after being indicted on human rights and tax evasion charges. Past attempts to prosecute the former dictator have failed when his attorneys argued that he was not healthy enough to stand trial.

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On the Net:

http://www.weisfeiler.com/boris/