Police have launched an investigation into allegations of sexual abuse at an Orthodox boys' school in Australia by a former teacher serving a seven-year prison term in the US.

David Kramer fled in the early 1990s after accusations he had sexually abused boys at Yeshivah College in Melbourne between 1989 and 1993.

Kramer, 50, was jailed in 2008 after pleading guilty to molesting a 12-year-old boy at a shul in St Louis, Missouri.

Victoria Police have now written to former Yeshivah College students asking for victims or witnesses to come forward.

Police may try to extradite Kramer when he is released from prison, which could be as early as next year, according to a report on Wednesday in Melbourne's The Age newspaper.

It is understood Yeshivah College asked Kramer, then a Jewish studies teacher, to leave after teachers were made aware of the allegations, which were never reported to authorities at the time.

In an open letter to the community this week, Yeshivah College parent Menachem Vorchheimer wrote that many have been aware of the allegations "for an extended period of time".

"We have a duty to confront sexual abuse in our community," he wrote. "Ongoing silence is not an option."

One Orthodox insider, who spoke on condition of anonymity, said: "There's no pressure any more to keep quiet. The Orthodox community worldwide has changed its attitude. The days of keeping it quiet are gone."

Last year, the Rabbinical Council of Victoria passed a resolution affirming its "unqualified condemnation of all forms of child abuse".

It stated that the prohibition on reporting crimes to authorities "does not apply in cases of abuse".

Another member of the Orthodox community said that the alleged victims were now adults, most with children, who may be too traumatised to relive the abuse. "My major concern is to ensure that paedophiles are stopped," said the man, who remembers sitting two rows away from Kramer in shul. "This is horrendous, but he's still entitled to the presumption of innocence."