Dorking, England (CNN) The mother of a British man accused of wanting to shoot Donald Trump says she fears her son will not survive a long period in prison.

The 20-year-old told investigators he wanted "to kill Trump." He faces up to a decade in jail if convicted.

Back home in England, Sandford's mother Lynne says she's worried the 20-year-old is not coping in custody.

"He's in pieces. He's broken. He's bewildered," she says. "He begs me not to hang up the phone when we do speak."

Struggle with mental illness

Speaking from their hometown of Dorking, south of London, Lynne Sandford says her son is the very opposite of a potential assassin, "a very sweet, very sensitive, soppy, loving lad."

Michael Sandford with his mother Lynne when he was a child; she says he was a "sweet, sensitive lad."

But Sandford's story reveals a deeply troubled young man who has long struggled with mental illness.

Lynne says her son was first diagnosed with autism aged 13; soon afterwards, doctors realized he also suffered from depression, anxiety, obsessive compulsive disorder and anorexia.

She says that, aged just 14, he was admitted to a London psychiatric hospital for four months because he had stopped eating.

"He'd just given up on himself. He'd lost the will to live. He found everything too difficult," she says.

Michael Sandford was diagnosed with autism, depression, anorexia and anxiety as a child.

Move to the US

At 18, Michael declared he was moving to the United States to be with a girlfriend. His mother says she was desperately worried but couldn't stop him, so the family agreed to help him financially.

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Lynne says her concerns increased quickly after he started living in New Jersey. He became increasingly evasive and vague about what he was doing, and only rarely made contact; eventually she discovered he was sleeping on the street.

"I had a text message from him saying, 'I can't live like this much longer,'" she says. "I just could not understand why he was not coming back."

Sandford's visa had expired and he was in the US illegally; he had been living out of his car in California for a month, CNN affiliate KSNV reports.

A short time later, the call came from the British government's foreign office telling her what had happened in Las Vegas.

"I was just shaking from head to foot and I burst into tears," she remembers. "My heart stopped, my mind was racing."

Visit to shooting range

Police say Sandford struck up a conversation with a Las Vegas police officer, under the pretense that he wanted to get an autograph, before attempting to pull the officer's gun from its holster

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He is accused of planning his actions that day for around a year, and of going to a shooting range in the city the day before the rally to learn how to handle a weapon.

He told investigators he thought he would be killed during the act.

He has been charged with being in an illegal alien in possession of a firearm and disrupting the orderly conduct of government business and official functions. He has pleaded not guilty.

"Luckily we're not looking at attempted murder," says Lynne. "Which I believe shows the police do acknowledge this wasn't a realistic attempt on Donald Trump's life."

Plea for treatment

Lynne Sandford holds a photo of her son; if convicted, she hopes he can serve his sentence in the UK.

The Sandford family is trying to raise money for legal and travel expenses through a crowd-funding campaign

His mother says they understand he must be punished for his actions, but that they want to see him serve his sentence -- and receive treatment -- in the United Kingdom.

"There's no getting away from what he did," she says. "He did attempt to do a very bad, very wrong thing.

"But he's not a bad person. That's why we want to get him back to the UK. We want to get him psychiatric help, and we want him to see his family."