(NewsNation) — Can you spot a killer? Can any of us identify warning signs that would prevent a mass shooting? These are questions being raised now more than ever in light of recent tragedies.

In trying to find answers to these critical questions, sometimes we have to look to the past.

Nearly a decade ago, James Holmes went inside a movie theater in Aurora, Colorado, and unleashed gunfire into a crowd watching “The Dark Knight Rises.” The shooting rampage left 12 dead, 70 hurt and sent shockwaves throughout the nation.

Ahead of the attack, there was another kind of terror. A psychiatrist said she knew she was dealing with an evil, troubled client, but could not find the legal means to protect the public from him.

Dr. Lynne Fenton spent months working with Holmes, getting a glimpse into the mind of a killer. When she started trying to treat the graduate student, the hair on her arms stood up.

“It was one of those terrible gut feelings without a lot of actual evidence that one of the best predictors of future violence is past violence. He wasn’t mean to animals. He didn’t beat up other kids. He never broke the law. He had none of the indications that a lot of, you know, so called psychopaths or antisocial folks will have,” Fenton said Tuesday on “NewsNation Prime.”

Even with the terrible gut feeling, Fenton never knew she would become the only psychiatrist in the history of the U.S. to be publicly revealed as the doctor of a mass shooter.

“He was so odd, and he had this vague thought of killing people. That’s how he put it, ‘I have thoughts of killing people.’ But it was so vague,” Fenton said. “I spent the months that I worked with him, six sessions total, trying to get him to talk more about that and understand. Is he capable of this? Is this just a thought of killing people? Or is he actually going to plan to go out and do it?”

As Fenton’s concerns surged, she says she contacted his mom and the police. She even brought a consultant into session to see if Holmes would open up more.

“After his last visit, I called his mom, even though the consultant and I specifically asked Holmes would it be OK if we called a family member or friend to learn more about how you’ve been doing? He refused. But when he walked out of my office, I just thought, ‘I have got to find out if he’s always been odd and strange like this, or is this a new thing? Is he having a psychotic break?’” Dr. Fenton said.

After speaking with his mother, Fenton says she felt a little reassured and that his behavior was not a sudden change.

In hindsight, she now believes Holmes was lying and manipulated her.

“Unfortunately, yes, I know that he was lying while I was seeing him because the last month, the month of May, and I last saw him on May 31. He was actually amassing weapons and ammo, and he was going to the shooting range and shooting up human figures. All the while denying … that he actually had plans to kill anyone,” Fenton said.

The aftermath of the tragedy was tough for Fenton.

“To some degree, I became kind of a scapegoat. People were thinking perhaps I could have prevented this somehow. (Neither) I, nor the university that employs me, could defend me and say the length I had gone to,” Fenton said.

Holmes is now behind bars and will spend the rest of his life there. In August 2015, he was sentenced to life in prison without the possibility of parole. The jury could not come to a unanimous decision on the death penalty.

Meanwhile, Fenton wrote a book titled “Aurora: The Psychiatrist Who Treated the Movie Theater Killer Tells Her Story” about her look into the psyche of a mass shooter, the inability to thwart Holmes’ violence and what it takes to place someone in a mental health hold. She hopes some of the information in the book may help prevent future shootings.

Fenton dedicated the book to the victims and survivors of James Holmes’ unspeakable atrocities for their courage and their voice.