Updated

Police officers who arrested James Holmes after the Colorado movie theater massacre described the suspected gunman as unusually relaxed but fidgety at times.

They also said at a preliminary hearing Monday that Holmes was clad in body armor, seemed detached and volunteered that his apartment had been booby trapped.

Prosecutors are laying out their case against the former neuroscience graduate student at the hearing.

Investigators say Holmes tossed two gas canisters and then opened fire during the midnight showing of the Batman movie "The Dark Knight Rises" on July 20, killing 12 people and wounding dozens.

The hearing is expected to last all week and will allow the judge to determine whether the prosecution's case is strong enough to warrant a trial.