Earlier reports suggested that there might be a second person of interest in the Colorado shooting case, but police confirmed that suspect James Holmes was the only one involved.

Aurora police interviewed an associate of the suspect, Holmes, who killed 12 people and injured 58 at the Century 16 movie theater in Colorado at a midnight screening of "The Dark Knight Rises" July 20.

"An associate of Holmes was interviewed this evening. There is no reason to believe that he is involved. Further details of this investigation will not be released at this time," Aurora police said in a statement.

The associate was found Friday and questioned Saturday night.

That same night, the Aurora Police Department received an electronic communication that threatened violence is Holmes wasn't released from jail.

According to ABC News Denver, the communication was traced through an internet protocol number to a router in Aurora. The person who lives at the address is an acquaintance of James Holmes through their program at the Anschutz Medical Campus, according to the sources.

Investigators are uncertain whether the person at the address actually sent the electronic communication or if someone routed it through that address. It was unclear whether the person actually sent the threat.

According to FOX31 Denver, sources told FOX31 reporter Justin Joseph that someone made either a call or a text from the person of interest's phone threatening violence if James Eagan Holmes was not released from jail. That call prompted police to issue an alert to find and detain him.

The associate's Facebook page shows he has a master's degree in bio-medical science.

Anshutz Medical Center confirms he is in their doctorate program, the same program from which Holmes withdrew several months ago.

However, the investigators interviewing him have gained more information about James Holmes, the sources told ABC.

Witnesses described Holmes kicking open the back door of the Century Aurora 16 theater and opening fire with four weapons, one AK-type assault rifle, a shotgun and two handguns, according to CNN. Wearing a bulletproof vest and goggles, he stood at the front of the theater, tossed tear gas into the crowd and starting randomly shooting.

Police found that his apartment was booby-trapped, and that the movie theater attack was planned with "calculation and deliberation," according to FOX News. Authorities eliminated all the explosives in the lethal apartment. No officials were injured, but the traps were "meant to kill" the first person who opened the door to the apartment, which was loaded with explosives.

Among the deceased victims was a 6-year-old Veronica Moser-Sullivan. She was at the theater with her mother, who was drifting in and out of consciousness in a hospital intensive care unit.

 Another victim, 27-year-old Matt McQuinn, was killed after diving in front of his girlfriend and her older brother to shield them from the gunfire.

Alex Sullivan died on his 27th birthday, which he was celebrating with a midnight showing of "The Dark Knight Rises," and a day before his first wedding anniversary.

FOX News reported that families grieved and waited at hospitals, which reported at least seven still in critical condition Saturday and others with injuries that likely are permanent.