CLACKAMAS, Ore. -- The man who killed two people and wounded another at Clackamas Town Center bought more than 100 rounds of ammunition in the days before the December attack.

That information is in a 926-page report the Clackamas County Sheriff's Office released Wednesday.

Photos: Clackamas mall shooting investigation

Investigators said 22-year-old Jacob Tyler Roberts, of Portland, was the lone suspect in the the murders of Steven Forsyth and Cindy Yuille, and the attempted murder of Kristina Shevchenko on December 11, 2012, said Clackamas County Sheriff Craig Roberts.

Click to read the CCSO timeline of events

All evidence consistently indicates that the suspect acted alone, Roberts said. The suspect died at the scene as a result of a self-inflicted gunshot wound.

The report shows he wore a hockey mask and carried an AR-15 semi-automatic rifle when he opened fire.

According to the documents, he stole the rifle from a friend that morning, and that he had bought four 30-round magazines and six boxes of ammunition days before.

A motive was not determined, despite interviews with hundreds of witnesses, family members, coworkers and friends of Roberts.

The documents did show that Roberts tested positive for marijuana and low levels of cocaine. He had no diagnosed mental illness.

The Clackamas County Sheriff's Office offers its sincere condolences to the Forsyth, Yuille, and Shevchenko families for the pain and losses they suffered, Roberts said in a statement Wednesday. We thank them for their cooperation and understanding during this investigation.

Background: Gunman, two victims die in Clackamas mall shooting

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