The mother of Chris Harper-Mercer, the shooter behind the deadly rampage at Umpqua Community College in Roseburg, Oregon, knew of her son’s fascination with guns and acknowledged in online posts that he struggled with mental illness, the New York Times reported Tuesday, citing the posts made over a decade.

Laurel Harper, a nurse, appears to have encouraged her son’s interest in guns and stored the weapons in their apartment, according to the Times. She reportedly wrote in a post that they both struggled with Asperger's syndrome, a form of autism.

“No one will be 'dropping' by my house uninvited without acknowledgement," Laurel Harper wrote in the post, according to the Times. She also reportedly indicated in an online forum that her son had extensive knowledge about firearms.

Investigators have previously stated that they seized 14 guns that were either with him or recovered from his home. Harper-Mercer stormed his writing class in Snyder Hall last Thursday, where he shot and killed his professor and eight classmates. He reportedly ordered individuals to stand, asked them their religion and then started shooting them. He committed suicide soon after officers arrived on the scene and exchanged fire with him.

According to Agence France-Presse, which cited the Times, Laurel Harper's posts were found on Yahoo Answers, a site where she spent hours over the last 10 years answering mainly medical questions.

Harper-Mercer’s mother also spoke with colleagues about her struggle to raise a son with mental health issues and about placing him in a psychiatric hospital in California, before they moved to Oregon in 2013.

"She said that 'my son is a real big problem of mine'," Alexis Jefferson, who worked with Harper at a care center in 2010, told the Times. "She said: 'He has some psychological problems. Sometimes he takes his medication, sometimes he doesn't. And that's where the big problem is, when he doesn't take his medication."

The shooting at Umpqua has revived the debate on gun control in the United States, prompting President Barack Obama to urge lawmakers to revisit the issue. Obama is scheduled to visit Oregon Friday to meet the victims’ families.

Meanwhile, Senate Democrats are gearing up to introduce new gun control legislation Thursday in the wake of the deadly Oregon school shooting. Democratic politicians have called for stricter gun control laws. Presidential candidate Hillary Clinton said this week that she would expand background checks at gun shows and ban domestic abusers from purchasing guns.