Christine CunninghamA knifepoint robber targeted vulnerable young male students travelling by rail making them hand over cash and even pay for his train fare.Christine Cunningham

A knifepoint robber targeted vulnerable young male students travelling by rail making them hand over cash and even pay for his train fare.

Adam Mustafa, 24, targeted a male student he met at Norwich station - just 10 days after he had threatened another student on a train from Sudbury to Colchester, making him buy his train ticket and then forcing him to go to a cash point machine before the student managed to get away.

Nick Methold, prosecuting at Norwich Crown Court, said that Mustafa had threatened the student on the Norwich to Cambridge train with a Stanley blade and had told him: "I'm not afraid to use it."

The terrified student handed over his wallet and mobile phone and Mr Methold said: "At that point he was too terrified to tell the guard what was happening."

It was only when he got off the train at Thetford station that he was able to raise the alarm and tell the transport police about his ordeal.

Mustafa, of no fixed address, was later arrested in Cambridge and admitted the two robberies in December 2008 and one charge of false imprisonment.

The court heard that Mustafa had a bad record, including four previous convictions for similar robberies, where young men he met on trains were made to hand over cash and go to cash point machines to withdraw money. For these offences he was given a hospital order and was released 11 months later but kept under supervision until November 2008 - a month before he committed these latest offences.

However a new detailed psychiatric assessment had shown that Mustafa was not suffering from any mental disorder which required treatment in hospital.

Judge Peter Jacobs imposed an indeterminate sentence for the protection of the public under which Mustafa must serve a minimum of three years and will not be released until the parole board considered he was no longer a risk, although Judge Jacobs said: "There is bound to be great public concern about releasing you."

Shakeel Jamil, for Mustafa, said: "Clearly this man does have mental health problems."

He said his motive for the robberies was get away from London on a train - but he had no cash. "This man never uses any actual violence."

He said by pleading guilty he had shown remorse.