For years, forensic psychiatrist Dr. John Bradford has been renowned as an expert in his field with a keen ability to look into the minds of criminals. But now Bradford is revealing that watching videos of the crimes committed by the likes of Paul Bernardo and Russell Williams led to a diagnosis of post-traumatic stress disorder. And he's warning that it could happen to others.

Over the course of his career, Bradford has seen videos that few others have: the footage that Paul Bernardo and his then-wife Karla Homolka took of their crimes, as well as the images of Russell Williams killing his victims.

Watching the videos was necessary for his job, but Bradford says he didn't realize the images were staying with him and eroding his own mental health.

"I think I first noticed things after the Bernardo video tapes," Bradford told CTV's Canada AM from Ottawa Thursday. "There was one particular scene in that that seemed to play over and over again in my head and that had audio with it."

Many others who watched the Bernardo videos were just as affected as he was; in fact, many jurors were offered counselling after the trial.

But Bradford thought he had remained detached from what he saw. His thoughts about the videos seemed to fade after a few months, he says, and while the memories sometimes resurfaced, he didn't think they bothered him.

"But then, when I was exposed to the Russell Williams videotapes, it really just hit me much harder," he said.

Viewing both the Bernardo and the Williams tapes, Bradford watched women being raped and listened to them pleading for their lives, knowing that they were about to die. Within 30 minutes of seeing the Williams tapes, Bradford says he began to have a breakdown.

"I was crying. I felt my life was a failure. And then the Bernardo and these tapes began to play in my head incessantly. And that's when I knew I had a problem," he remembers.

At first, he tried to convince himself that he was fine and that he could stay professional. But he says his struggle with what he had seen began affecting his personal life too.

"At home, I started to become more irritable, I wasn't sleeping. I become much more unreasonable, and constantly struggling with emotional issues that make life very difficult," he recalled.

Looking back, Bradford says he realizes he spent months in denial of the problem that he had.

"I thought I was this sort of tough guy and that this was part of the job. I didn't quite realize that I needed treatment," he says.

It took more than a year, but Bradford eventually sought the help of a trusted colleague who eventually diagnosed him with post-traumatic stress disorder (PTSD).

Bradford says the diagnosis came as a shock, since he had long believed that only those who had experienced or personally witnessed a trauma could develop PTSD.

"I didn't even realize that the videos could have this type of impact on you," he says.

Bradford agreed to undergo counselling and began taking medication more than a year ago, both of which he says have helped. Through the counselling, he says he learned that he has "certain vulnerabilities. "

He's feeling "a lot better" now and working again, but Bradford says there are still certain precautions he still needs to take to protect his mental health.

"In my case, I'm being careful what I do, and so anything to do with videos I avoid at the moment," he says.

He now wants to warn others who do what he does or who work in similar fields that this is something that can happen to them too, that even witnessing the images of crimes can be damaging.

"It's very important for other people exposed to this – police officers, social workers working with videos of these types of situations – that they need to be careful," Bradford says. "Because if it can happen to me, it can happen to anybody."