Roberts' mother, Tami Roberts, released a statement through a friend today saying she had no explanation of her son's behavior.
"Tami Roberts wishes to express her shock and grief at the events at Clackamas Town Center Tuesday," the friend said, reading from a statement outside of Tami Roberts' home.
The friend noted that Tami raised Roberts, but was not his biological mother. Sansburn said that Roberts' biological mother had died when he was very young.
"She has no understanding or explanation for her son's behavior...It's so out of his character," the friend said.
Officials from the Oregon City School District, where Roberts graduated from Oregon City High School, were also surprised at the news.
"This news is very shocking to those who knew Jacob while at OCHS. He was known as a soft spoken and polite young man who was often eager to be helpful. The motive for such a horrific act is likely to remain a mystery to us all," the district said in a statement.
Roberts had attended the school for only his senior year. He spent three years at Milwaukie High School, where officials described him as an "average student with average grades."
He had no disciplinary record at the school, but chose to transfer for his senior year to Oregon City High School, according to Joe Krumm, an administrator at the North Clackamas School District. Krumm did not know why he transferred, and said that in all, Roberts did not stand out in memory for anything in particular.