(UPI) -- Residents of the Aurora, Colo., apartment building where alleged theater gunman James Holmes lived are being allowed to return to their homes, officials said.

Police remained on the scene overnight for security purposes, CNN said Wednesday.

The tenants were evacuated Friday after Holmes was arrested for the massacre at the midnight premiere of the Batman movie "The Dark Knight Rises" that killed 12 people and wounded dozens more. Holmes told police there were explosives in the apartment.

The one-bedroom apartment was rigged with 30 homemade grenades and 10 gallons of gasoline, law enforcement officials told CNN.

Holmes, who identified himself to police as "The Joker" is being held without bond. Formal charges are expected Monday.

Foxnews.com reported a package sent to the University of Colorado -- Anschutz Medical Campus in Aurora, where Holmes had recently been a student, was found Monday. The package, addressed to a psychologist at the university, contained a letter in which Holmes allegedly detailed his plans to shooting people.

Seventeen patients remain hospitalized, six in critical condition.

The Denver Post said the Public Defender's Office combed the suspect's apartment Wednesday.

Dan Recht, a criminal defense attorney who is not involved in the case, said the attorneys were likely trying to get a better sense of their client. He suggested the attorneys would be looking for signs of mental illness, such as deranged writings or drawings, the newspaper said.

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