Aurora, Colo., shooting suspect James Holmes came to the attention of the threat assessment committee at the University of Colorado but no further action was taken because he left the school more than a month before the attack that killed 12 and injured 58, sources told ABC News.

ABC News has learned that Dr. Lynne Fenton, the psychiatrist who was treating Holmes, 24, at the school, was also a key member of the university's threat assessment team. The group of experts were responsible for protecting the school from potentially violent students.

KMGH-TV, ABC News' affiliate in Denver, reported exclusively that, according to sources, by early June, Fenton had informed other members of the team about her concerns regarding Holmes.

But on June 10 -- three days after Holmes bought an assault weapon and added it to his already growing arsenal -- he suddenly told the university that he was dropping out of the neurosciences doctoral program with no explanation.

KMGH-TV reported last week that he'd purchased the weapon hours after failing a key oral exam.

On Monday, Holmes was charged with 24 counts of first-degree murder in the fatal shooting during a midnight screening of "The Dark Knight Rises."

Twelve people were killed and 58 were wounded in the worst mass shooting in U.S. history. Each death carried two separate murder charges, one for showing premeditation and one for showing extreme indifference to life. Both of the charges carry the death penalty as a possible sentence.

Sources have told KMGH-TV that the threat assessment team never had a formal meeting and never intervened, believing that it had no control over Holmes once he'd left the university. Documents uncovered by ABC News show that Fenton also wrote the school's policy on threat assessment.

Michael Carrigan, chairman of the CU board of regents, told KMGH that he did not know if Holmes had ever been discussed by the threat assessment team. "It's the first I'm hearing about this," he said in a phone interview.

A CU spokeswoman declined comment to KMGH on Fenton or any threat-team team actions, citing a gag order.

Don Elliman, the university's chancellor, said last week that "to the best of our knowledge, at this point, we did everything we think we could have done."

But experts said today that Holmes' departure should have been a red alert.

"You know, I think that's the signal that you should intensify your efforts, not walk away," said Barry Spodak, a threat assessment expert. "Under those circumstances, most well-trained threat assessment teams would have gone into action."