ABC News' Carol McKinley and Clayton Sandell report:

Accused Aurora movie theater shooter James Holmes is expected to enter a plea next week, sources told ABC News, after his legal team lost an attempt to challenge the constitutionality of Colorado laws governing mental health defenses and insanity pleas.

In motions filed last week, public defenders asked Judge William Sylvester to answer a series of legal questions, including whether or not a court-ordered mental evaluation could be used against Holmes if he entered a plea of not guilty by reason of insanity, but later withdrew it.

"In order to effectively represent Mr. Holmes, counsel must be able to accurately assess the consequences of a plea of not guilty by reason of insanity," his attorneys wrote.

Prosecutors argued there were no constitutional issues to settle, pointing out that public defenders in two previous and unrelated cases filed similar motions that were denied.

"Defendant has not met his burden to show any of the statutes he challenges are unconstitutional," prosecutors wrote in a motion filed by District Attorney George Brauchler's office.

In an order filed late Thursday, Sylvester largely ruled against Holmes' legal team, investigative sources told ABC News.

A court spokesman, who had not seen Sylvester's ruling and could not comment on what it said, confirmed that prosecutors and defense teams received copies of the order Thursday evening. Attorneys on both sides did not respond to ABC News' requests for comment.

Unless the defense team decides to appeal it, the judge's ruling sweeps aside potentially time-consuming legal wrangling that threatened to delay an arraignment hearing set for March 12, when Holmes is expected to enter a plea.

Holmes, now 25, is charged with 166 counts, including murder, attempted murder and explosives charges, after prosecutors say he opened fire July 20 during a crowded midnight showing of "The Dark Knight Rises". Twelve people were killed and 58 were wounded by gunfire. Another 12 people sustained other injuries.

Prosecutors have not said whether they intend to seek the death penalty. Holmes has not entered an insanity plea, but his attorneys said he "is considering" the option.

Defense attorneys not involved with the case said that by raising constitutional questions, Holmes' lawyers may be trying to "build a record" that might help them in potential future appeals.

"Many things are filed to preserve the defendant's right to appeal," said Denver defense attorney Larry Pozner. "If you don't ask, you can't complain later."