Adrian Lamo says jail for WikiLeaks suspect would be a 'lasting regret' but stands by decision to give information to authorities

Adrian Lamo, the hacker who betrayed the alleged WikiLeaks source Bradley Manning to the US authorities, has said it would be to his "lasting regret" were the soldier to be given a lengthy custodial sentence.

Lamo, 30, dubbed the "world's most hated hacker" for his role in passing information on Manning to military intelligence after the soldier befriended him on internet chat, said that he understood that Manning was an idealistic young man who believed he could change the world for the better and "who didn't necessarily know what he was doing.

"I think about him every day. The decision was not one I decided to make, but was thrust upon me."

Lamo's comments come on the eve of the opening of a pre-trial hearing in the prosecution of Manning, who is charged with multiple counts of transferring state secrets to WikiLeaks including hundreds of thousands of US embassy cables. The hearing starts in Fort Meade, Maryland, on Friday amid exceptionally tight security.

Bradley Manning supporters hoping for an expression of remorse from Lamo ahead of the soldier's prosecution will be disappointed, however. Despite the note of regret at a possible harsh sentence for Manning – the soldier faces a maximum punishment of life in custody with no chance of parole – Lamo said he continued to be convinced that he had done the necessary thing.

"Had I done nothing, I would always have been left wondering whether the hundreds of thousands of documents that had been leaked to unknown third parties would end up costing lives, either directly or indirectly," he said.

A soldier alleged to be Bradley Manning contacted Lamo on AOL instant messaging on 21 May 2010, using the internet handle Bradass87. Lamo was known to the soldier because of his celebrity status in the hacking world having been prosecuted in 2003 for breaking into the computer network of the New York Times, for which Lamo was put on six months' house arrest.

In the course of their internet chat, later published by Wired, the soldier asked Lamo: "if you had free reign [sic] over classified networks for long periods of time, things that belonged in the public domain, what would you do?" The soldier confessed to Lamo that he had been downloading US state secrets on to a CD labelled "Lady Gaga".

Lamo took advice from two friends who had experience working with military intelligence, and, with their assistance, he passed the details of the internet conversation to the US military. On 26 May, Manning was arrested on duty at the Forward Operating Base Hammer outside Baghdad, where he was working as an intelligence officer.

For his action, Lamo was denounced by fellow hackers as a "snitch" and a traitor to the community, and was booed at the Hackers On Planet Earth conference in Manhattan in July 2010. Lamo said he also had to move home to avoid any opprobrium affecting those close to him.

But he said he was unflustered by the adverse reaction. "I'm not a politician running for re-election. I don't need to be popular among the hacker community, and I most likely will never be liked in the hacker community."

Lamo said he was taken aback by the enormous fallout from his approach to the military authorities. "At the time I was not even certain that this was newsworthy. I suppose that demonstrates a certain degree of naivety on my part."

He had thought hard, he said, about Manning's position. "I remembered what it was like to be Manning's age – 22 – that was the age that I was arrested for what I regarded as crimes of conscience. I deliberated on whether I wanted to subject someone of that age to the same process that I went through."

In the end though, he concluded that "Mr Manning's wellbeing was not as important as the security of our armed forces. I had never considered myself particularly patriotic, but when push came to shove the wellbeing of the nation was of paramount importance to me."

He said he suffered "a great deal of internal conflict" about Manning's situation when he was being held at the Quantico marine base in Virginia. The soldier was held in solitary confinement and stripped naked every night in conditions that some likened to torture.

Manning, 23, is now being held under a much more liberal regime at Fort Leavenworth in Kansas.

Lamo declined to speculate about what an appropriate sentence would be for Manning were he found guilty of the WikiLeaks charges. However, a hypothetical individual who had engaged in passing state secrets to a third party would merit a sentence of "25 to 50 years", he said.

"This is different to a James Bond film. WikiLeaks was involved in an overall weakening of strategic operations and diplomacy that will take decades to recover from," he said.

But Lamo added that he was aware of the lasting harm that he has caused. "There are times in life when you are faced with a variety of choices, none of which you consider right. All of them harm someone and you have to choose the one that harms the fewest number of people. That still leaves you harming someone, and, because of that, I think of Manning on a daily basis."