A convicted killer who murdered a man with learning difficulties during a botched robbery on a corner shop was jailed for life yesterday.

The victim had been looking after the store while his family attended his brother's passing-out parade at Strathclyde Police training college.

Judge Lady Clark of Calton said John McGeechan, 47, must remain behind bars for at least 20 years after stabbing Amjid Ismail.

After the verdict, Mr Ismail's family called for an urgent review of the justice system, saying McGeechan should never be freed or transferred to an open prison.

McGeechan, jailed 12 years ago for killing a friend who threw snowballs at his dogs, fled from the store in Maybole, Ayrshire, taking only the phone Mr Ismail, 34, had tried to use in a vain attempt to call for help, despite his injuries.

However, the victim had wrongly dialled his home when he tried to phone police. No-one was in when he made his desperate call, but the answering machine at the house recorded the murder.

Customers later found Mr Ismail bleeding from a knife wound to his neck. Doctors at Ayr Hospital were unable to save him. "On any view, this was a wicked crime," said Lady Clark.

Mr Ismail was looking after the shop while the rest of the family went to see younger brother Anjam become a police officer. Another brother, Amir, was at the High Court in Edinburgh to see McGeechan sentenced.

Afterwards, he said: "Nobody can understand just how heart-breaking and soul- destroying it is to come home and find your parents in tears, night after night, week after month, in the knowledge that there is nothing you can do to assist. There is no doubt in my mind that the individual responsible for this crime is an evil, cold and pathetic coward.

"There are no circumstances whatsoever in my mind that may justify an individual convicted of taking the life of another person even being considered for early release or placement within an open prison.

"The time has surely now come for our Members of Parliament to be accountable to the public and launch an urgent and immediate review of the various elements of our justice system, with swift legislation to address the changes sought."

At the end of McGeechan's trial, the court heard that it was his second fatal stabbing in 12 years. In 1996, he admitted culpable homicide after stabbing 24-year-old Martin Siegerson for throwing snowballs at his dogs in Cranhill, Glasgow. McGeechan served a total of more than nine years of a 10-year sentence.

He denied demanding money from Amjid Ismail on the afternoon of November 8, 2006, at Kirkland Stores in Maybole, then inflicting a total of eight stab wounds.

McGeechan claimed he had an alibi, but a jury found him guilty. McGeechan, formerly of Kirkland Street, Maybole, went to prison yesterday - still protesting his innocence.

Lady Clark told him: "You showed no mercy or concern for the victim. You used a knife repeatedly against a defenceless victim at his work. He sustained terrible injuries."

The judge added: "This is the second time you have appeared in these courts when you have caused a death."

The shop has not opened its doors since the day of the murder.