A neighbor of the man authorities say killed at least nine people at an Oregon community college Thursday told reporters the gunman "seemed really unfriendly."

Bronte Harte told the Associated Press she lived in the apartment below 26-year-old Christopher Harper Mercer in Winchester, Ore. Winchester is approximately five miles north of Roseburg, where Mercer opened fire in a classroom at Umpqua Community College, killing nine people before being killed in an exchange of gunfire with responding officers.

Harte said Mercer would often "sit by himself in the dark in the balcony with this little light." She added that a woman she believed to be Mercer's mother also lived upstairs and was "crying her eyes out" Thursday.

Harte also told the New York Times Mercer would frequently yell at her for smoking on her apartment's balcony.

"He yelled at us, me and my husband," Hart told the paper. "He was not a friendly type of guy. He did not want anything to do with anyone."

More On This...

KPTV reported that investigators had sealed off the Winchester complex and had established a search perimeter. Officers at the scene were escorting residents to and from their apartments. A sheriff's deputy told a resident that there was no danger to the community and people living in the apartments around where Mercer lived were able to access their homes.

Authorities were attempting to establish a motive for Thursday's shooting. It was not immediately clear what, if any, connection Mercer had to the college, a two-year school with an enrollment of just over 3,000 students.

Law enforcement sources told Fox News that Mercer's name was being run through watchlists and his email history, phone logs, social media profiles and online history were being checked in an effort to rule out any links to international terrorism.

A law enforcement official told the Los Angeles Times that Mercer was armed with three handguns and an assault rifle when he carried out the shooting. The official did not know whether Mercer fired all the guns, or where and how he obtained them.

Mercer was born in England and moved to the Los Angeles area with his parents when he was a young boy, law enforcement sources told Fox News.

Before moving to Oregon in 2011, Mercer lived with his mother in an apartment complex in Torrance, Calif., located just southwest of downtown Los Angeles. Local media reported that neighbors who lived near the pair in Torrance said they often saw Mercer wearing camouflage pants and large, black boots.

Mercer's father, Ian Harper, briefly spoke to reporters outside his home in Tarzana, Calif. late Thursday. He said he had spent the day speaking to police and other authorities. Harper declined to answer any questions about his son.

"Shocked is all I can say," Ian Harper said. "Obviously it’s been a devastating day, devastating for me and my family." 

One neighbor, Derrick McClendon, told the Los Angeles Times that Mercer was "bashful" and "timid", adding that the young man mostly kept to himself.

"I wouldn't have suspected for him to be a troubled person," McClendon said.

Other neighbors told the paper that they sometimes noticed Mercer and his mother carrying matching black cases that appeared to contain firearms. The paper said that some neighbors asked Mercer about the weapons at a community barbeque, to which Mercer responded that he liked to go target shooting.

"I don't know what to say," Carmen Nesnick of Tarzana, Calif., identified as Mercer's stepsister, told KNBC. "I'm shaking right now. He was a nice guy."

Fox News' Catherine Herridge, Matt Dean, Jonathan Hunt and The Associated Press contributed to this report.