A security guard at the Family Research Council's headquarters in Washington, D.C. is being hailed as a hero after he stopped a gunman posing as an intern, taking a bullet in the arm before wrestling the suspect to the ground.

The gunman, identified as 28-year-old Floyd Lee Corkins II, entered the lobby of the organization's Chinatown headquarters around 10:45 a.m. and expressed disagreement with the conservative group's policy positions, sources tell Fox News.

When the guard asked him where he was going, he opened fire, according to police.

“The security guard here is a hero, as far as I’m concerned,” D.C. Police Chief Cathy Lanier said. "He did his job. The person never made it past the front.”

[pullquote]

The guard, Leo Johnson, was shot in the arm and was conscious after the shooting and in stable condition. Corkins was being questioned by the FBI, sources said. Sources said he lives in Herndon, Va.

The suspect "made statements regarding their policies, and then opened fire with a gun striking a security guard," a source told Fox News.

Sources also said the gunman may have been carrying a bag from Chick-fil-A, the embattled fast-food restaurant whose president came under fire from gay activists after he said he did not agree with same-sex marriage.

Sources told Fox News that after guard took away his gun, the suspect said, "Don't shoot me, it was not about you, it was what this place stands for."

Authorities were treating the attack as a case of domestic terrorism, although James McJunkin, the head of the FBI’s Washington Field Office, said authorities do not yet know the gunman's motive.

“We don’t know enough about him or his circumstances to determine what his connection is to this group [the research council] or his mental state, or what he was doing or thinking of doing,” McJunkin said. “So we’re going to try to sort this all out, pull the evidence together, do all the interviews we can.”

Corkins had been volunteering for about the past six months at The DC Center for the LGBT Community, said David Mariner, executive director of the community center, which is in Northwest Washington. He usually staffed the center's front desk on Saturdays, and his most recent shift was about two weeks ago.

"He always struck me as a kind, gentle and unassuming young man. I'm very surprised that he could be involved in something like this," Mariner said.

The FRC is a conservative nonprofit that seeks to advance "faith, family and freedom in public policy and public opinion," according to its website. The group weighs in on policy, and has often sent representatives to Congress to weigh in on the social effects of policy matters.

“The police are investigating this incident," Family Research Council President Tony Perkins said. "Our first concern is with our colleague who was shot today. Our concern is for him and his family.”

Advocacy groups across the ideological spectrum condemned the violence, with some casting it as a hate crime.

"Today's attack is the clearest sign we've seen that labeling pro-marriage groups as `hateful' must end," Brian Brown, the president of the National Organization for Marriage, said in a statement.

White House spokesman Jay Carney said the president, who was traveling in Iowa Wednesday, was informed of the shooting shortly after 1 p.m.

"The president expressed his concern for the individual injured in the shooting and his strong belief that this type of violence has no place in our society," Carney said.

Republican presidential candidate Mitt Romney said in a statement that he was appalled. "There is no place for such violence in our society," he said. "My prayers go out to the wounded security guard and his family, as well as all the people at the Family Research Council whose sense of security has been shattered by today's horrific events."

Fox News' Mike Levine and The Associated Press contributed to this report.