Important evidence in the case of Gary McKinnon, the north London geek who hacked into the Pentagon's computers, has disappeared from his lawyers' office, the Evening Standard reveals today. Notes of meetings at the American Embassy, in which a diplomat suggested prosecutors in the United States wanted McKinnon to "fry", also vanished when a solicitor's laptop was stolen.

The mysterious disappearances were disclosed by McKinnon's mother, Janis Sharp, speaking for the first time after the House of Lords rejected his appeal against extradition to stand trial for what one American prosecutor described as "the biggest military computer hack of all time". The Americans claim he penetrated 97 military computers at the Pentagon and Nasa between February 2001 and March 2002.

They want to charge him with stealing passwords and rendering security systems inoperable. Prosecutors have warned they may treat him as a terrorist and, his mother says, only intervention by the European Court of Human Rights can save him from a possible jail sentence of up to 70 years. "I feel Gary is fighting for his life," she said. "I am terrified about the threat to 'fry' him. I think the Americans will stop at nothing to make sure he never embarrasses them again."

This impression was reinforced by the disappearance of documents related to McKinnon's case. Janis, a 59-yearold musician and film-maker, said: "They wanted Gary to go to a meeting at the American Embassy in London. I said to him: 'For goodness sake don't go inside that building! That is American soil and if they get you in there, they can do as they like.' So his solicitor went and had meetings with prosecutors who had flown over especially."

At one of these meetings, Janis said, the lawyers were told that if McKinnon went to the United States voluntarily he would be treated leniently and could expect a sentence of between 18 months and three years, most of which he could serve in the UK. Then, she said, threats were made.

"They said that if Gary didn't go they would treat him as an enemy combatant. They said the prosecutors in one state wanted him 'to fry' - be executed - and in any case he would be looking at 60 to 70 years in jail."

The US prosecutor could offer no meaningful guarantee of leniency and McKinnon's legal team formed a view that the menaces were an abuse and an attempt to force him to abandon his rights. Janis said: "The two lawyers at the meeting took very careful notes. When it became clear those notes would be evidence in the future, the papers vanished."

McKinnon's lawyer, Karen Todner, a founder partner in Kaim Todner, a law practice with a head office in the City and branches elsewhere in London and the south, said she attended three meetings at the American Embassy with the legal attaché present.

DURING these meetings, she said, it was indeed suggested that if McKinnon did not go voluntarily he could be treated as a terrorist and prosecutors would be looking for a maximum sentence of up to 70 years.

"The legal attaché told me that the prosecutors in one state wanted Gary 'to fry'. That was the phrase he used. I made a note of it, and everything else that had been said." Ms Todner was accompanied by a solicitor colleague who made notes of the conversation on his laptop.

Shortly after this, she said, the notes of the meetings disappeared from McKinnon's file, held in her City office. Nothing else was taken and there was no obvious sign of a break-in. Then her col league ' s l aptop, which also contained the notes, was stolen from his car.

"It's very easy to get carried away with conspiracy theories in a case like this," Ms Todner said. "But after our experience with this disappearing evidence, I have to say - who knows?"

Evidence that shows the Americans want to deal with McKinnon, 42, as if he were a terrorist is significant because it invokes the prospect of Guantanamo Bay and arraignment before a military tribunal, with the possibility of pre-trial abuse for which America has been condemned by Human Rights campaigners.

Janis says this clearly demonstrates a disparity in her son's treatment by the justice system here. A British court recently refused to extradite Abu Qatada, described as Osama bin Laden's spokesman in Europe, to Jordan because of fears over the treatment he might receive there.

"My son is not al Qaeda," she said. "He is not the enemy - he is not even political."

Britain's extradition arrangements with the United States were overhauled in 2003, ostensibly to streamline the processing of terrorist suspects. Janis claims the Americans have exploited the 2003 Extradition Act to try to get hold of her son.

The law is controversial because it makes it significantly easier for America to secure extradition from Britain, while the treaty that underpins it has not been signed in Washington and probably never will be.

The arrangement has been increasingly used against white-collar crime suspects. It was used to get the Natwest Three to the United States to stand trial and last month Ian Norris, a 65-year-old former City executive, lost a court battle against extradition by the same route.

Critics say the law is entirely onesided and was another symptom of the Labour Government's eagerness to demonstrate fealty to George W Bush.

In 2006 the Daily Telegraph ran a campaign against the law, describing it as "manifestly unfair".

Now McKinnon's legal options have almost expired. Janis says only an appeal to the European Court of Human Rights can save him. "I am desperately worried about rendition," she said. "The way this case has been handled makes me think the Americans could snatch him off a street in London, put him on a plane and the authorities here would do nothing."

Janis and her husband, Wilson, an illustrator who has been Gary's stepfather since Gary was six, are articulate, creative people. That may be why they encouraged Gary to become interested in computers at such an early stage.

"We got him one of the first Ataris when he was about 10," Janis said. "He took to it straight away. Then he got a later model and by the time he was in his early teens he was programming it."

His other passion was for unidentified flying objects. When the internet opened up, McKinnon - by then a computer professional - began using the web to search for evidence that UFOs really do exist. It became an obsession. He would spend long nights at his then girlfriend's flat in Crouch End, smoking cannabis, roaming cyberspace, seeking the Holy Grail of the UFO fanatic: a photograph of an alien spacecraft. McKinnon says he found one, but was unable to download it.

Janis says she believes him. "I had no idea what he was doing at the time," she said. "I knew he was spending too long shut up with the computer and I'd tell him to get out, get some fresh air. He said: 'Don't worry. I'm OK.'"

But McKinnon wasn't OK. Consumed by a suspicion that the American Department of Defense was hiding evidence of extraterrestrial beings, he was staying up all night, forgetting to eat and wash. It was a haggard, barely coherent man who discovered one night in 2001 that he could penetrate the Pentagon.

Using software bought on the internet, he began hacking into the US military's computers. On a Nasa computer housed in the Johnson Space Center in Houston, Texas, he said he found a grainy black and white image he believes was a photograph of a craft from another planet. Before he could download it his connection was snapped shut.

Whatever judgments are made about people with an unshakeable belief in extraterrestrials, it is an acknowledged fact that McKinnon managed to break into the innermost workings of the American military.

WHEN I asked him how he did it, using a shop-bought dial-up connection, he made it sound terrifyingly easy. "In many cases no passwords were set," he said. "Either there were no firewalls, or the firewalls thought I was on the inside and they let me in. They were running a Windows protocol that allowed me to log on with software that was available off the shelf."

He was tracked down when he became careless and, he readily admits, very stupid. He started creating his own passwords for the Pentagon's IT systems and left teasing notes about the shambolic security. At one point he posted a message that suggested the 9/11 atrocities were "an inside job".

After that, Janis said, the security apparatus of the world's only superpower was directed to hunting him down. As McKinnon began his fight against extradition his personal life collapsed. He split from his girlfriend and lost his job. Now he lives with a new partner, in Palmers Green.

"He is not allowed to use the internet," Janis said, "and he's got no chance of getting a flat of his own." He was working as a fork-lift driver, but that, too, became impossible to sustain as he devoted his energies to his case.

After his arrest in 2002 by the UK's High-Tech Crime Unit he spent a night in Brixton jail, but was given £5,000 bail. Janis said the sum reflected the British authorities' relatively relaxed view of his alleged crime. The police told him he might get six months, but the Crown Prosecution Service decided not to bring a case.

"We hoped it had all blown over," she said. Then, after the 2003 extradition deal was ratified, the Americans made their move.

McKinnon should know within a week or so whether the European court will take his case. If it does, current backlogs could mean he will be safe from extradition for at least two years and, if he wins, the decision to extradite could be overturned.

In the meantime, Janis believes America wants to close her son down, permanently, one way or another. For most of us, he may be a dotty obsessive, but to the dark masters of the Pentagon he is a man who knows too much.

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