Police say Batman shooting suspect James Holmes is refusing to co-operate with authorities.
Aurora police chief Dan Oates said 24-year-old Holmes had “lawyered up” and was not talking.
Holmes, said to have carried out one of the worst shootings in US history, was arrested after the gunman opened fire during a midnight screening of The Dark Knight Rises, killing 12 people and injuring 58.
He has been appointed a public defender and is due to make an initial court appearance today.
Mr Oates said it could take months to determine a motive and police were working with FBI behavioural analysts.
The police chief said Holmes had more than 50 commercial packages delivered to his home and school address during the past four months.
Holmes is due to appear in court today at 9.30am (4.30pm Irish Time).
Police said Holmes began buying guns at Denver-area stores nearly two months before the shooting and received at least 50 packages in four months at his home and at school.
Yesterday a gun club owner east of Denver said he recently rejected a membership application from Holmes in part because of a “bizarre” voicemail greeting on his phone.
The University of Colorado said it was co-operating with police in the case, but it remained unclear whether Holmes’ professors and other students at his 35-student PhD programme noticed anything unusual about his behaviour.
His reasons for dropping out of the programme in June, just a year into the five to seven-year course, also remained a mystery.
The university declined to release any details of his academic record, citing privacy concerns, and at least two dozen professors and other staff refused to speak to the press. Some said they were instructed not to talk publicly about Holmes in a blanket email sent to university employees.
Jacque Montgomery, a spokeswoman for the University of Colorado medical school, said police had told the school not to talk about Holmes. The university also took down the website for its graduate neuroscience programme on Saturday.
Ritchie Duong, who has known Holmes for more than a decade, told the Los Angeles Times that in high school he liked to play cards and video games. They both attended undergraduate school at the University of California, Riverside, where they saw each other once a week to watch the TV show Lost.
Mr Duong, 24, last saw Holmes in December when they met for dinner in Los Angeles and saw a film together. His friend seemed fine, he told the newspaper. Academic subjects came easily to Holmes both at high school and at the UC Riverside, Mr Duong said.
“I had one college class with him and he didn’t even have to take notes or anything. He would just show up to class, sit there, and around test time he would always get an A,” he said.
The pastor for the family of the suspect also recalled a shy boy who was driven to succeed academically.
“He wasn’t an extrovert at all. If there was any conversation, it would be because I initiated it, not because he did,” said Jerald Borgie, senior pastor of Penasquitos Lutheran Church. Mr Borgie said he never saw the suspect mingle with others his age at church.
Holmes told the pastor he wanted to attend a University of California school and pursue graduate studies.
“He had some goals. He wanted to succeed, he wanted to go out, and he wanted to be the best,” Mr Borgie said. “He took pride in his academic abilities. A good student. He didn’t brag about it.”
The family had belonged to the church for about 10 years, Mr Borgie said. His mother Arlene attends services every week and is a volunteer.
Friday’s shooting was the worst in the US since the November 5, 2009, attack at Fort Hood, Texas. An army psychiatrist was charged with killing 13 soldiers and civilians and wounding more than two dozen others.