By Keith Coffman

DENVER (Reuters) - The University of Colorado has hired a former federal prosecutor to probe its handling of a former graduate student accused of killing 12 people and wounding 58 in a shooting spree at a movie theater in a Denver suburb, the school said on Friday.

Robert Miller was retained to conduct an internal review of the university's dealings with accused gunman and former neuroscience graduate student James Holmes, the university said in a written statement.

Holmes was charged this week with 24 counts of first-degree murder and 116 counts of attempted murder for the shootings at the July 20 midnight showing of "The Dark Knight Rises" in Aurora, Colorado.

Questions have arisen about what the university knew about Holmes' mental state in the weeks leading up to the massacre.

His attorneys said a court filing that he was a patient of Dr. Lynne Fenton, a psychiatrist who is medical director for student health services at the university's Denver campus.

The judge presiding over the case has imposed a gag order preventing involved parties from publicly discussing the case, but Fox News, citing an anonymous source, reported that Holmes had sent a notebook, which was not opened, to Fenton detailing his plans for the massacre.

Also citing anonymous sources, the Denver Post reported Thursday that Fenton had notified the school's threat assessment team about behavior by Holmes, 24, that she found alarming.

Miller is a former U.S. Attorney and Judge Advocate General for the U.S. Air Force who is now in private practice.

"They have been asked to assess various university systems, procedures and actions related to the suspect," the university said.

The review, which began last week, was requested by University of Colorado Denver chancellor Donald Elliman, who earlier said he believed university personnel "did what they should have done" in dealing with Holmes.

"Our resolve rests with understanding all the facts so we can assist law enforcement and other authorities in ensuring that justice prevails," Elliman said in a statement announcing the review.

The university put no timeline on Miller's report, and said it is unclear how much of the information it could release publicly because of the gag order and student privacy laws.

Holmes, who authorities say told police that he was the Joker, in reference to Batman's comic-book foe, is being held in solitary confinement and without bond in the Arapahoe County jail.

(Editing by Dan Whitcomb and Jackie Frank)