Opening arguments set in US Batman shooting trial

 Opening arguments will take place next week in the trial of James Holmes, the gunman accused of killing 12 US cinema-goers at a 2012 screening of a Batman movie, AFP reports.

The long-awaited trial will finally get under way in earnest on Monday, three months after the process of jury selection began, officials said Tuesday.

The 27-year-old has pleaded not guilty by reason of insanity, but could face the death penalty if convicted.

Holmes has been in custody since the night of July 20, 2012 in Aurora, Colorado, and faces 166 counts of aggravated murder, attempted murder and possession of explosives.

Witnesses say Holmes threw smoke bomb-type devices before opening fire inside the Century theater with weapons including a military-style rifle, a shotgun and a .40-caliber pistol. Seventy people were also wounded.

His one-bedroom apartment was later found to be booby-trapped with an array of homemade explosive devices which police had to disarm before entering.

In preliminary hearings prosecutors said Holmes, a neuroscience graduate student, had in his possession sufficient ammunition to kill everyone in the crowded theater showing "The Dark Knight Rises."

Holmes stunned observers by appearing in court initially with flaming orange hair similar to the Batman character The Joker. Later, he wore jail scrubs with brown hair and a heavy beard. In January he looked markedly different, sporting a neatly trimmed beard, dark brown hair and dark-rimmed glasses.

The trial began in January with jury selection to pick 24 jurors and stand-ins from a selection pool of over 9,000 Denver-area residents.

The primary issue at trial will be whether Holmes was sane at the time of the massacre.

He has undergone two separate psychiatric examinations since his arrest and much of the trial is expected to be devoted to psychiatric testimony.

The high-profile trial could run through September or October in the event of a guilty verdict. Colorado law requires a two-phase trial, the first assessing guilt or innocence; the second focusing on punishment.