In his new book "The Good Nurse" Charles Graeber details the life of serial killer Charlie Cullen who posed as a nurse in hospitals and then injected patients with lethal doses of a variety of medications.

Charlie Cullen, known as the nation's most prolific serial killer, was arrested in a hospital after he was found injecting patients with lethal doses of a variety of medications. He has reportedly killed hundreds of people in nine different hospitals in a span of 16 years.

Journalist Charles Graeber spent six years investigating the Cullen case, and is the only reporter to have spoken with Cullen in prison. In his new book "The Good Nurse", Graeber pieces together the elements of Cullen's story.

On the actions of the hospitals

"The first actions you see time and time again at these hospitals is a legal action rather than an effective investigative reaction. And oftentimes, you'll find that what becomes - certainly in retrospect - to be a real burden of evidence against one guy ... when it starts to really look like this guy is dirty, that's the time he gets moved on one way or the other. He's pushed out or pressured out. So do the hospitals know? That's a question a reader needs to ask, and I think I provide enough evidence that they'll be able to draw that conclusion. But certainly he should have been stopped before he was, and because he wasn't, he killed a lot more people."

On Cullen's troubled childhood, possible sexual abuse and his first attempt at murder

"When asked directly about abuse of that sort in the house he gets very angry. He has gotten very angry with family members, with ex-wives, when they've tried to get him to seek counseling, when they've tried to take him aside, because the pattern - it certainly seems to fit the pattern. He won't say, but he felt unsafe. There were strange men in and out of that house. He had a brother-in-law that came to live with one of his sisters when his sister was pregnant. There was a lot of domestic abuse surrounding that. Exactly what happened to the child is not clear. Eventually the sister ran away, but the brother-in-law stayed, and he and Charlie had a tortured relationship that Charlie had reported to at least one - if not two - of his later lovers that he'd tried to poison that brother's drink. He'd put lighter fluid in the vodka, which is sort of an early example of what would become his pattern for life: a way of passively dealing with things."

On Cullen's narcissism

"His thinking is circular, narcissistic and then the question is how far does that narcissism go? Is it sociopathic? And the answer to that lies somewhere in, well, you have to ask yourself, 'What sort of a person can kill someone and be there as they die and not have it seem to really affect their day at all, or in fact affect their future behavior in any negative fashion for 16 years?'"

On Cullen's hero complex

"Sometimes that's what worked for him. He knew what was wrong with a patient when no one else did. He could be the first to go in there. The other residents remember him jumping on the chest of a patient in just - the sort of - the most dramatic fashion. They appreciated his enthusiasm and his passion, but it seemed a little over the top. But the truth was he did what others could not do, and he did receive praise for that. It did elevate his status, and so there was absolutely an element of ego in the murders."