The loner suspected of killing Jo Cox appeared deeply disturbed just 24 hours before the attack, a health counsellor said last night.

Thomas Mair said after stumbling into a 'well-being centre' on Wednesday night that he was depressed and had been on medication for a long time.

Mair's psychiatric history is at the heart of the police inquiry into the attack – and officers are also said to be investigating links to far-Right groups.

The counsellor who spoke to him for about 15 minutes on Wednesday said she realised he was in 'some sort of crisis' and there appeared to be a 'real problem'.

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Tragedy: Jo Cox died in the arms of one of her assistants after being shot. Mrs Cox leaves two children, aged three and five

Thomas Mair (left) has been arrested over the killing of MP Jo Cox (right). Mair's psychiatric history is at the heart of the police inquiry into the attack – and officers are also said to be investigating links to far-Right groups

The next day, the unemployed gardener was arrested after allegedly shooting and stabbing the Labour MP to death outside her constituency surgery in West Yorkshire.

Neighbours said the obsessive recluse was often seen wandering around the town and had not received any formal mental health treatment for five years.

Counter terrorist detectives are also said to be probing his links to Right-wing extremism after a hoard of neo-Nazi memorabilia and literature was apparently found at his home.

It emerged yesterday that Mair bought a manual on how to build a home-made gun from a far-Right group in the US.

Mrs Cox's husband Brendan last night changed his Twitter profile picture to a photograph of his wife with their children

Vigils have been held across the UK in memory of Jo Cox as people were urged to honour her legacy by building a world with 'more love and less hate'

From left: Ed Miliband, former deputy leader Harriet Harman and Wes Sweeting joined members of the public at a vigil in front of the Houses of Parliament

Thousands of people stood solemnly in silence in Parliament Sqaure in London, to remember the MP

As investigators worked around the clock to uncover what lies behind the tragedy:

■ One of Mrs Cox's closest aides revealed how she said 'I can't make it, I'm in too much pain' as she died in her arms;

■ The brave have-a-go hero stabbed in the stomach as he attempted to tackle the gunman was revealed to be a retired coal mine rescue worker;

■ Parliament was urgently recalled so that grieving colleagues could pay tribute to the rising Labour star;

■ David Cameron stood shoulder to shoulder with Labour leader Jeremy Corbyn to mark an extraordinary national outpouring of grief;

■ An angry row grew amid claims a Labour MP tried to politicise the tragedy by criticising the 'dangerous material' published by the Leave campaign;

■ A fund opened by Brendan Cox in memory of his wife met its £50,000 target in less than three hours as donations flooded in.

Mair remained in custody at a West Yorkshire Police station last night as the force conducted a wide-ranging inquiry into his background.

The suspected killer was said to be 'lucid' when first questioned after being found fit for interview by two police doctors.

He was arrested in the street just minutes after Mrs Cox, 41, who was walking to her regular constituency surgery, was attacked in a busy Birstall shopping street.

He was in some sort of crisis

Her assistant, Fazila Aswat, 38, turned around to find her lying between two cars covered in blood as the gunman threatened bystanders with a knife.

Her father, Labour councillor Gulham Maniyar, said the killer then moved closed to the MP, firing a further shot at her head.

A gun, now believed to be a sawn-off shotgun, and other weapons, including a large machete-style knife, have been recovered.

Mrs Cox leaves two children, aged three and five, and Mr Maniyar said her husband Brendan was struggling to come to terms with his loss.

Mrs Cox, 41, is pictured with her husband Brendan on election night when she was elected as an MP for the Batley and Spen area (left) and posing happily with her husband on their wedding day (right)

Thousands of people gathered for a vigil in Parliament Square in remembrance of the Labour MP

'I just think about her two beautiful children,' he said. 'Her husband told my daughter on the telephone 'We haven't told the children yet, what am I going to tell them tomorrow?'.' The Daily Mail has learned Mair walked into a centre which provides alternative therapies and counselling the evening before the shooting.

Staff said he came into the private business – 100 yards from the murder scene – asking what treatments he could have.

Rebecca Walker, 43, who spoke to him for about 15 minutes, said she realised he was in 'some sort of crisis' She said: 'He said he had walked by the centre every day for years and wanted to come in but never did.

'He has never had the courage to come in. He suffered with depression and said he had been on medication for a long time.'

Left, A framed photograph of MP Jo Cox and her husband outside 10 Downing Street has been placed among the floral tributes near the murder scene. Right, the much-loved MP pictured in her wedding dress

Two hours after her death, Mrs Cox's heartbroken husband Brendan tweeted a photo of her standing by the houseboat they stayed on when they were in London

Miss Walker said he seemed a 'quiet and gentle man' and added: 'I couldn't believe what has happened.'

She said: 'He was clearly have some kind of crisis. I think there was a real problem. He made a choice to come inside when he had never been able to do that before.'

All MPs have been urged to review their personal security in the wake of the attack, which came after concerns were raised about stalkers last year.

Mrs Cox had been targeted by malicious messages from two individuals, one of whom was cautioned by the Metropolitan Police. Neither are linked to her death.

The National Police Chiefs' Council said every police force will contact their local politicians to ensure they are responding to 'any specific threat or risk'.

West Yorkshire Police Chief Constable Dee Collins said: West Yorkshire Police Chief Constable Dee Collins said murder squad detectives are working alongside counter terrorist officers on the inquiry.

'Based on information available at this time, this appears to be an isolated, but targeted attack upon Jo.'