One of the heroes of yesterday's London Bridge attack is a convicted murderer out on day release, it has emerged.

It is believed James Ford rushed to the scene and tried to save the life of a woman victim of the terrorist. Now 42, Ford was jailed for life – with a minimum of 15 years – in April 2004 for the murder of a 21-year-old with learning difficulties.

Amanda Champion – who had the mental age of a 15-year-old – was found strangled and with her throat cut on waste ground near her home in Ashford, Kent, the previous July.

Left: One of the heroes of yesterday's London Bridge attack is a convicted murderer out on day release, James Ford. Right: Amanda Champion – who had the mental age of a 15-year-old – was found strangled and with her throat cut

Police had no leads in the case until a Samaritans worker broke the organisation's strict confidentiality policy and revealed that Ford, a factory worker and amateur wrestler, had called and confessed: 'I've killed a girl.'

In the month after murdering Amanda, Ford phoned the charity line 45 times, telling staff he was feeling suicidal. After he admitted his crime, the Samaritans worker – who was later forced out of his job – decided to go to police.

Amanda's family had tried to block Ford's parole, and only found out he had been released from his sentence in a call from their police liaison officer today.

Whitehall sources confirmed that Ford – who had been serving the final days of his sentence at HMP Standford Hill, an open prison in Kent – was on London Bridge yesterday.

Video filmed at the scene shows at least four people struggling with a man at London Bridge

Amanda's aunt Angela Cox, 65, was left shocked and angry after the phone call from Kent Police.

Despite Ford's part in disarming the knifeman, she said: 'He is not a hero. He is a murderer out on day release, which us as a family didn't know anything about. He murdered a disabled girl. He is not a hero, absolutely not.

'The police liaison officer called me saying he was on the TV. I am so angry. They let him out without even telling us. Any of my family could have been in London and just bumped into him.

'It was a hell of a shock. It is a horrible thing. She said, 'Have you heard about the incident in London today?' and I hadn't. She said, 'Put in on now and you will see James Ford on the telly.'

'She said, 'Don't worry, it is not him that's done anything, he's there and he is being classed as a hero.' For him to be called a hero – he is not, he is a cold-blooded murderer. For no reason whatsoever, he just went out and murdered a disabled person. I don't care what he's done today, he's a murderer. He is scum. Amanda was my niece and she was vulnerable and he took her life. He knew what he was doing. People don't change.'

Ford has never revealed his motive for killing Amanda.

A judge told him: 'What you did was an act of wickedness.

'You clearly have an interest in the macabre and also an obsession with death including murder by throat cutting.

'Amanda happened to be walking through that area of woodland at the wrong time. You grabbed hold of her, strangled her and cut her throat, causing her to suffer a terrible and lonely death.'

A Kent Police spokesman said at the time: 'James Ford is a very dangerous man.'

Last night the Ministry of Justice declined to comment.