An era is passing in New York with the retirement of the legendary prosecutor who was the model for the district attorney on the TV programme Law and Order.

Robert Morgenthau has announced that he will step down at 90 after almost 35 years in office, rather than run for a tenth term in November.

The Manhattan district attorney has brought more than three million prosecutions against everyone from the mob chieftain John Gotti to John Lennon's killer, Mark David Chapman.

Celebrities often found themselves in his sights, from the phone thrower Russell Crowe and short-tempered supermodel Naomi Campbell to rapper Sean “P. Diddy” Combs and the singer Boy George.

Mr Morgenthau, the son of President Franklin Delano Roosevelt's Treasury Secretary, grew up surrounded by America's political elite.

He once cooked hot dogs with Eleanor Roosevelt for King George VI, and prepared a mint julep for Winston Churchill.

In the Second World War he spent hours treading water in the Mediterranean after German bombers sank his destroyer.

In 1960 Mr Morgenthau campaigned for his boyhood friend John F. Kennedy for president. Once elected, President Kennedy appointed him federal prosecutor for New York.

But President Nixon threatened to sack him if he did not step down, and he left the post in 1970. After running unsuccessfully for New York governor against Nelson Rockefeller, he was elected Manhattan DA for the first time in 1974.

Mr Morgenthau improved the conviction rate from 73 per cent to nearly 90 per cent. His targets included the infamous subway vigilante Bernard Goetz, who was convicted of weapons charges for shooting four black men he thought were going to rob him on an underground train in 1988.

But Mr Morgenthau did not always succeed. John Gotti, the “Dapper Don”, who ran the city's largest crime family, beat the rap. So did P. Diddy, acquitted of gun charges after a shooting in a nightclub.

Perhaps his biggest black eye was the overturning of convictions against five youths in the rape of a Central Park jogger after new evidence emerged. Dick Wolf, the creator of Law and Order, said that Mr Morgenthau was the model for the original prosecutor, played by Steven Hill. “He was the inspiration for the Adam Schiff character when I created Law and Order and it worked out very well,” he said.

At the last election in 2005, Mr Morgenthau faced a challenge from a female former judge who tried to make an issue of his advanced years. But he still mulled a run this time around, with the slogan “90 in '09”. Mr Morgenthau said: “Some people are slow to learn. It took me a long time to realise I was getting older.”

“I don't know what I'll do. I got an e-mail from my older brother, who said this is a bad time to be looking for a job,” he quipped.

His departure has set candidates running to replace him. Daniel Castelman, Mr Morgenthau's long-serving deputy, who has played the role of a mob prosecutor on The Sopranos, quit abruptly this week when his boss refused to endorse him as his successor.

Mr Morgenthau is expected to endorse Cyrus Vance, a former prosecutor who is the son of President Carter's Secretary of State.

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