Ed Pilkington investigates the use of the death penalty in America Photograph: guardian.co.uk

Ed Pilkington: Let's start with the reason we're having this IM chat: Bradley Manning. We heard Manning himself recently describe his treatment during the nine months he was held in Quantico marine base on suspicion of having leaked hundreds of thousands of confidential US documents and videos to WikiLeaks. Have you been following the proceedings, and if so how closely?

Adrian Lamo. Photograph: Jennifer S Altman/Washington Post/Getty Images

Adrian Lamo: My only exposure to the proceedings right now is the things that people ask me whether I've heard. That sometimes disturbs folks' sense of perspective, as though it's wrong of me to have more to my life than Bradley Manning. It's not because I take it lightly, but because I take it as seriously as I do. Making the choice to interdict a man's freedom knowing it could mean his life, is something that's easy to judge but can only really be understood by living it. You either fold it into your character, come to terms and go on with your life, or you get stuck in that moment forever. For a while I thought I would be. I took it badly. But I came to terms and continued my life some time ago. It has, after all, been two years.

EP: We heard harrowing testimony from Manning. Locked in his 8x6ft cell for 23 hours and 40 minutes a day, stripped naked at night, made to stand to attention at morning call in the nude. And on and on … I appreciate that you might not want your life to be stuck on Manning, but hearing such details must have an impact on you. Did you expect him to face such harsh treatment when, as you put it, you chose to interdict his freedom by passing his details to the FBI?

AL: As a clarification, I co-operated with the Department of Defense in this matter, not the FBI. This is the army's prosecution, and while there's some overlap, the FBI is looking at another spectrum of issues. To speak to your question, I don't have first-hand knowledge of his conditions while detained. But a lot of choices by a lot of people went into taking this case where it is today. It's clear the circumstances would be very different if it weren't for my involvement, but you can only label something a proximate cause within so many degrees of separation of what it's putatively causal of.

Even so, as I stated, I knew my actions might cost him his life. In that respect, any other outcome is preferable.

EP: OK, so let's go back in time and look at what happened in May 2010. Why in your view did Manning pick you out of the cybersphere to be his confidant?

AL: There are a lot of possible reasons, but only he knows which one moved him. With something so speculative, there's no real right answer.

EP: It has been suggested by some of your critics that you did not innocently engage in the web chat with Manning, but that you were somehow put up to do it as a sort of honey trap. Were you?

AL: Heh. I needed a good laugh. Not being sarcastic, it's just so very implausible. The logs are not in dispute. It was suggested otherwise for a long time, but the proponents of that idea – [former hacker] Kevin Mitnick for one – have gradually found fresher theories to push. Looking at the interaction going in, he's eager to disclose what he's done, while I'm at points almost uninterested at first – wandering away from the keyboard at various points.

But more pragmatically, the cast of characters is just bizarre. You have me, you have Kevin Poulsen [of Wired magazine, which published the web chat] writing the story, and then a good number of my long-time associates in other key roles later on. If you wanted a situation that didn't seem outlandish, that ain't it. The way it played out seems like something that could only happen in a movie, not anything you could propose as covert action with a straight face.

EP: It's clear from the web chat that he was crying out to you for help. "I'm honestly scared," he said. "I have no one I trust. I need a lot of help." How did you feel when you read that?

AL: His statements there – and others, such as his reference, seemingly in half-jest, to having his firearm ready after I mentioned (I think) that I'd been away from the keyboard for a phone call, and his anecdote about striking a fellow soldier – did seem to indicate personal issues which might be coming to a head. But however I personally felt about his issues, his motives, and his state of mind didn't matter, and could not factor into what I did. The choices at hand were very blunt ones – to interdict him, or to pretend I'd never had my conscience as shocked as it was when I learned of the sheer volume of sensitive documents he had extracted to WikiLeaks.

There was no option to interdict just the documents and put him merely in touch with counseling. There was no way to be both kind to Bradley and mindful of the potential for harm to people I had never known and would never know which the situation posed. The reader might think there was some more moderate choice that I overlooked but I looked closely, and no such choice existed.

There's a science fiction story from 1954 or so by Tom Godwin, called The Cold Equations. It's about, in summary, a space shuttle, a stowaway, a pilot, and a far-off research station. Specifically, about a young girl who's stowed away not realizing that her slight excess weight would doom the flight of badly-needed medical supplies unless she was ejected. At its heart, it's a story about how much we might feel for someone and how little human feeling means against the weight of numbers. There were hundreds of thousands of documents – let's drop the number to 250,000 to be conservative – and doing nothing meant gambling that each and every one would do no harm if no warning was given. In the story, the stowaway is ejected from an airlock not because no one felt for her, but because everyone felt for her, wanted to help her, but all those feelings didn't matter a damn against the reality of the situation.

EP: Early on in your chat with Manning you reassured him about your trustworthiness, telling him you were a journalist and a church minister and that either way he'd have legal protection against his identity being revealed. That was clearly misleading, as things transpired, and your critics have accused you of lying to Manning by promising him protection. Do you regret having done that?

AL: Professionally and personally speaking, it's not my function to have people arrested. That's something that would ideally fall to law enforcement. In this matter, the harm from the subject's continued freedom appeared to objectively be greater than the harm of interdicting him. The offer was never meant to be construed as a suicide pact, and no one had ever mistaken it for one.

In the specific context of the logs, it's also relevant to note that the offer was never affirmatively accepted – it proposed two possible conditions, and one was never chosen.

EP: I want to press you on this point. If a priest, or a journalist, promises to protect someone's identity or confession, they can't then turn round and say: 'Oh, you've told me something bad, therefore I'm going to turn you in.' By telling Manning you would protect him (whether or not he accepted your offer) didn't you make pact, a vow, that couldn't be broken? If I tell a source of mine that I will protect his or her identity, I mean it.

AL: The two choices aren't fungible. They're distinct things, each with their own set of boundaries. In each case the law relating to privilege has exemption for exigent situations as the conscience sees them. Assuming the offer had been taken up and we'd gone forward – if I'd been a doctor or a counselor, the same would have been true – the law recognizes that privilege is not, as I said, a suicide pact. Meaning that once you enter into it, you're not bound to it no matter how much harm will arise. I'd have a much harder time saying with a straight face: "Well, he told me about the largest classified material breach in the history of western intelligence, but I wasn't supposed to tell anyone."

EP: What you've just said, and what you write in an article which the Guardian is posting along with this IM chat, hinges on the idea that by leaking state secrets to WikiLeaks, Manning was likely to cause great harm. But Manning made clear in his dialogue with you that he was in the process of being discharged from the military and that his security clearance had been restricted. Didn't that suggest that the threat he posed – to the extent it existed – was in the past?

AL: I think it's pretty clear that from a computer security standpoint – as some might say, from the standpoint of a hacker – there's no such thing as revoked access, only more complicated access. The threat only existed in the past from the point where he was interdicted on. His detention provided the United States with months of warning on the disclosures that were to come – months to prepare for the threat which those would pose which would not otherwise have been afforded to them. The details of that warning took Manning with them. One could not be separated from the other. I'm satisfied that such an early warning was both necessary and critical in mitigating the harm done.

EP: But in making that decision to sound an early warning – by going to the DoD – weren't you setting yourself up as judge and jury over Manning? And if so, what gave you the authority to make that judgment any more than Manning himself, or for that matter WikiLeaks?

AL: At age 13, I was violently mugged at a busy train station. There were dozens of onlookers, but none of them lent a hand. It was as though they couldn't see what was obviously happening in front of them, and if they did, couldn't justify to themselves the risks of getting involved. That was a defining point in that stage of my life. After that, I could never tell myself that it was someone else's problem, or let a situation pass me by if I felt something had to be done. I knew from experience that all too often, no one else would act.

My authority was that I was the only person who could make that choice. I knew that people would fret about what might have been, would second-guess, offer alternatives in hindsight. People always do. And invariably, none of those who do were there for the situation as it unfolded, or had to make that choice – have probably never had to make that kind of choice about a human life. But they're sure they know what they would have done, if only they'd been lucky enough to be there.

EP: In your piece you say you were faced with making a "cold, needful" choice. Yes, but … you are also a human being. It can't be possible purely to intellectualize a decision of that magnitude. After all, as you said earlier in this IM, you thought at the time you shopped Manning that he could face the death penalty. So tell me, honestly, in yourself, what were you thinking, feeling knowing that you might at that moment be sending a man to his death?

AL: To a greater or lesser extent, we all do things in life that we don't really want to. We might avoid it when possible, but we can't do it all the time. The very definition of irresponsibility is avoiding unwelcome choices wholesale. I'm sure I had feelings about it at the time. But now, over two years later, I can't tell you what that was like.

To your more gentle-hearted readers, that might seem quite monstrous. It might have to me at one point. But as smart and as prepared as I thought I was, there was simply no way to understand how the mind bends to adapt itself without living it. No way to explain it at all.

EP: "I was badly off for a while," you say. I can imagine you were. You were denounced as a "snitch" and the "world's most hated hacker". I think you've even said you were forced into hiding. So how are things now? Have things got better for you after more than two years? Can you tell us, for instance, where you're living now, or are you still keeping out of the public eye?

AL: Most of my daily life comes and goes without involving WikiLeaks or Bradley Manning. My security situation remains complicated, but not for the same reasons as a year or two ago. In many ways it's better. I had quite the substance abuse problem for a while. That's hardly unknown, and I'd feel dishonest doing this IM without speaking to it. I was in a period of recovery when I first met Brad, but as with such periods in many people, it didn't last, at least not that particular time. But coming to grips with how I felt about the whole situation helped to put a stop to that, helped me to cope on my own. Ironically, that's one of the best things to happen in my life in recent years, both in my personal and professional life. In contrast to that, having to keep my eyes open doesn't trouble me much. I'd always been one to keep my eyes open.

EP: Just a couple of final questions before we wrap. They both involve that wonderful thing, hindsight. In hindsight, isn't it the case that actually the data that Manning leaked, massive in quantity though it was, did very little damage at all? And that it did a lot of good – take for instance the exposure of Middle East corruption, and the video of the US Apache helicopter attack on civilians in Iraq which WikiLeaks released as "Collateral Murder"? So wasn't your assessment of the damage that the leaks would cause, in hindsight, over-dramatic?

AL: Not long after the files were released, the Taliban announced that they were combing poorly redacted contact logs for the names of Afghani nationals who were assisting security forces in postwar Afghanistan. Even if that were the sole data point, I'd remain convinced that months of warning is a hell of an important thing to give someone before the date of their potential execution.

WikiLeaks has a history of hand-waving away the consequences of their disclosures. When documents they released were linked to violence in Kenya, Julian Assange said, apparently to the Observer, that "1,300 people were eventually killed, and 350,000 were displaced. That was a result of our leak," going on to compare those numbers to the statistics of other deaths in Kenya – to paint death as a normal part of Kenyan existence, as it were.

Assange went on to say "… we are not about to leave the field of doing good simply because harm might happen", and that if anyone were conclusively killed because of WikiLeaks, they could take comfort knowing: "Well, we will review our procedures" upon proof of their death. I have a different vision of good, one where high ideals don't excuse any crime or atrocity because someone meant well.

EP: One final question based on hindsight. With everything we now know – including the way Manning was subjected to treatment that the UN likened to torture, and the fact that though he won't face the death penalty as you initially feared he does face possible life in military custody – would you make the same decision again?

AL: People are always asking me whether I'd have done the same if I'd known [x] or had foresight of [y]. Questions like that sound good in theory, but ultimately what they're asking is: "If linear time collapsed into itself and you were suddenly aware of every possible outcome, what would you do?" The thing is, it's not a question that can be answered. One of the great things about life, I think, is that we don't get do-overs. I don't think idealism could survive if we did.

Let me ask you for example, before this conversation, had you ever heard of a man named Frank Wills?

EP: No, can't say I had.

AL: Wills was the security guard at the Watergate in June 1972. Depending on how you look at it, he was either in the right place at the right time, or should never have gone to work that day. He died at the age of 52, in poverty after problems seeking employment due to his connection to the incident. He died five years before the identity of "Deep Throat" Mark Felt was revealed, but his death merited only a cursory obituary on page B7 in the regional section of his local paper. From his point of view, would he have made the same choice again? I'm not going to try to answer that. No one could.