(NBC News) - The gunman who shot Christians in the head at a Oregon college after asking for his victims' faiths appeared to be sympathetic to the predominantly Catholic Irish Republican Army — but also posted online that he was "not religious."

Former acquaintances and social-media postings paint a picture of 26-year-old Christopher Harper Mercer — who was killed in a firefight with police at Umpqua Community College on Thursday — as a withdrawn young man who spent a lot of time on the Internet.

Public records show that one person of that name was born in Los Angeles County in 1989. Police declined to confirm the shooter's identity late Thursday, in an attempt to not "glorify" the actions of the gunman behind a rampage that left 10 dead and seven others wounded.

Investigators said it was too soon to identify a motive, though Douglas County Sheriff John Hanlin told NBC's TODAY he wasn't aware of any "specific red flags" for the shooter.

"He is a local resident and I know personally I haven't heard of any warning signs coming from this person," Hanlin said.

A Myspace page that appeared to be linked to the shooter featured Mercer holding what appeared to be a rifle while several other postings were sympathetic to the Irish Republican Army and featured masked gunmen and logos.

The IRA is a predominantly Catholic paramilitary group which waged a bloody three-decade campaign to make Northern Ireland an independent republic separate from Great Britain. It was responsible for terrorist attacks in Northern Ireland and England, including an attempt to assassinate British Prime Minister Margaret Thatcher by bombing a hotel in 1984. More than 3,600 people were killed in the armed conflict.

The Myspace account — which is listed under Chris Harper-Mercer — also featured a formal photo with a caption reading "me in a tuxedo on the day of my sister's wedding."

A man listing the same birthday — and whose photo strongly resembles Mercer — also held a profile on a dating and penpal site for "spiritual singles" that listed Los Angeles as his location.

"Looking for someone who shares my beliefs, and is similar to me," the profile says, listing "Internet, killing zombies, movies, music" and reading among hobbies and interests.

The profile describes "not religious, but spiritual" beliefs and was linked to a group called "doesn't like organized religion."

Survivors of the Umpqua shooting told relatives that Harper Mercer asked people whether they were Christian or not. Anyone who responded "yes" was shot in the head and those who said "other" or didn't answer were shot elsewhere in the body, said Autumn Vicari, whose brother was in the classroom.

Sci-fi and horror were listed as favorite types of movies on the Myspace profile — along with romantic comedies.

The profile described the poster as "shy at first, but warm up quickly" and "better in small groups" — consistent with what Mercer's acquaintances said.

Former neighbors in the Los Angeles suburb of Torrance confirmed that Mercer lived with his mother in a downstairs apartment before moving to Oregon about four years ago.

Bryan Clay said he'd encounter the shooter "every day" when he'd come home from school — and that Mercer kept to himself.

"I'd see Chris, shaved head, combat boots, camo pants and a plain brown or white shirt," Clay told NBC Los Angeles. "He would really just walk really fast, avoid anybody who came towards him."

Mercer's father, though, told NBC Los Angeles his son was a "nice guy" who "put everyone before himself."

An online public records search for Chris Harper Mercer shows one man by that name having lived in Torrance before moving to an apartment in Winchester, Oregon — just 2.1 miles from Umpqua Community College. NBC News could not immediately verify whether it referred to the gunman.