A man who opened fire inside the headquarters of the conservative Family Research Council in Washington last year because of its opposition to same-sex marriage pleaded guilty Wednesday to committing an act of armed terrorism.

USMS

Floyd Lee Corkins

The man, Floyd Lee Corkins II, 28, of Herndon, Va., shot the council's unarmed security guard in the arm before he was subdued Aug. 15. He faces a maximum of 30 years in prison when he's sentenced April 29 on the three charges he admitted in the plea deal, which also included interstate transportation of a firearm and ammunition, a federal offense, and assault with intent to kill while armed, a local offense.

According to an FBI affidavit (.pdf), Corkins said, "I don't like your politics," as he opened fire. It also said he was carrying at least 50 additional rounds of ammunition in his backpack, along with 15 Chick-fil-A sandwiches.

The incident came a few weeks after Dan Cathy, chief executive of the fast-food company, said he opposed same-sex marriage and in the wake of reports that the company's charitable foundation had made millions of dollars in donations to organizations fighting efforts to legalize same-sex marriage.

The Family Research Council, an evangelical Christian activist group, came out strongly in support of Cathy's statements. Authorities said Corkins was a volunteer for a Washington organization lobbying for gay and lesbian rights.

Despite his injuries, the security guard, Leonardo Johnson, wrestled Corkins to the ground and gained control of the weapon while a second security guard called 911. Washington Police Chief Cathy Lanier called Johnson, who recovered, a hero, saying: "He did his job. The person never made it past farther than the front door."

Tony Perkins, president of the Family Research Council, blamed the shooting on civil rights organizations "that have been reckless in labeling organizations hate groups because they disagree with them on public policy." But a coalition of organizations promoting gay, lesbian and transgender rights joined other conservative activists in condemning the attack.

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Updated at 5:50 p.m. ET: WASHINGTON -- The president of the Family Research Council, whose employee was shot in the group's Washington, D.C., office, said on Thursday that a civil rights group bears some responsibility for the shooting. The rights group called the claim outrageous.

Floyd Lee Corkins II, age 28, of Herndon, Va., was charged in the Wednesday shooting.

"Floyd Corkins was responsible for firing the shot yesterday that wounded one of our colleagues and our friend," Tony Perkins said. "But Corkins was given a license to shoot an unarmed man by organizations like the Southern Poverty Law Center that have been reckless in labeling organizations hate groups because they disagree with them on public policy."

Perkins said the shooting victim, Leo Johnson, is not simply a security guard but is, in fact, the group's building manager, does not wear a uniform and does not carry a gun.

Told in the hospital Wednesday night that he was considered a hero, Johnson responded to Perkins, "This hero business is hard work."

The Southern Poverty Law Center has been strongly critical of the Family Research Council, and the two groups have been waging a public debate against each other for the past several years.

The SPLC's senior fellow Mark Potok called the comments by Perkins "outrageous":

"The SPLC has listed the FRC as a hate group since 2010 because it has knowingly spread false and denigrating propaganda about LGBT (lesbian, gay, bisexual and transgender) people -- not, as some claim, because it opposes same-sex marriage. The FRC and its allies on the religious right are saying, in effect, that offering legitimate and fact-based criticism in a democratic society is tantamount to suggesting that the objects of criticism should be the targets of criminal violence.

"We criticize the FRC for claiming, in Perkins' words, that pedophilia is "a homosexual problem" -- an utter falsehood, as every relevant scientific authority has stated. An FRC official has said he wanted to 'export homosexuals from the United States.' The same official advocated the criminalizing of homosexuality.

"Perkins and his allies, seeing an opportunity to score points, are using the attack on their offices to pose a false equivalency between the SPLC's criticisms of the FRC and the FRC's criticisms of LGBT people. The FRC routinely pushes out demonizing claims that gay people are child molesters and worse -- claims that are provably false. It should stop the demonization and affirm the dignity of all people."

Court documents accuse Corkins of walking into the council’s headquarters and telling a security guard words to the effect of "I don't like your politics."  The documents said Corkins drew his gun and shot the guard in the arm before the guard subdued him. Another guard called police, they said.

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Local and federal investigators gather evidence after a security guard was shot in the arm at the headquarters of the Family Research Council on Wednesday in Washington, D.C.

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Authorities said Corkins was carrying a handgun, two additional loaded ammunition clips, and a box of 50 more rounds.

Also in his backpack, they said, were 15 Chick-fil-A sandwiches.

Investigators said his parents told the FBI that their son "has strong opinions with respect to those he believes do not treat homosexuals in a fair manner."

Earlier: Security guard shot at conservative group's DC office

The Family Research Council strongly opposes same-sex marriage and abortion. Corkins had worked as a volunteer at a Washington center for homosexuals, bisexuals and transgender people.

Perkins sent an e-mail to members last month in support of comments by the restaurant chain's president, Dan Cathy, who criticized same-sex marriage.

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Corkins appeared briefly in federal court earlier Thursday. He was ordered held without bond, and a public defender was appointed to represent him.

Corkins is in FBI custody as part of a probe into whether the shooting could be considered a hate crime, the FBI has said.

Pete Williams is NBC News' chief justice correspondent.

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Updated at 6:45 p.m. ET: A gunman who shot a security guard Wednesday at the Family Research Council office in Washington, D.C., was carrying a handgun and several additional rounds of ammunition, federal investigators told NBC News. 

Washington, D.C., police say the man walked into the headquarters of the conservative Christian lobbying group around 10:45 a.m. When challenged by the security guard, the gunman shot the guard in the arm with a Sig Sauer 9 mm handgun he pulled from a backpack.

The wounded guard, identified as Leo Johnson, wrestled the gun away from the shooter and prevented him from hurting anyone else, police said.

The suspect was then detained by other guards, and both district police and the FBI responded. He was taken into custody by FBI agents. The FBI will have jurisdiction if the incident turns out to be a hate crime.

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Members of the FBI enter the Family Research Council office after a shooting Wednesday in Washington, D.C.

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The suspect’s name has not been released, but two law enforcement officials told NBC News he is Floyd Corkins, 28, from nearby Herndon, Va.

Federal officials said the suspect the backpack also contained materials about Chick-fil-A restaurants.

Another official said the suspect bought the gun used in the shooting five days ago.

The FBI said the security guard is being treated in the hospital and "doing OK."

“The security officer here is a hero, as far as I’m concerned,” Metropolitan Police Department Chief Cathy Lanier told NBCWashington.com. “He did his job. The person never made it past farther than the front door.”

Jacqueline Maguire, FBI Washington Field Office spokeswoman, also called the guard "a hero."

"And he did an excellent job of stopping the gunman from getting any further into the building and from anyone else getting injured or shot by him," she said.

One law enforcement official told NBC News it's fairly clear the Family Research Council was the man's target, though the FBI has yet to specify either a motive or the target of the attack.

The Associated Press reported that Corkins had been volunteering at a community center for gay, lesbian, bisexual and transgender people. Another official told the AP the shooter made a negative reference about the work of the Family Research Council before opening fire.

Tony Perkins of the Family Research Council sent an e-mail to members last month in support of comments by the restaurant chain's president, Dan Cathy, who criticized same-sex marriage.

The comments touched off a public clash. Supporters on "Chick-fil-A Appreciation Day" on Aug. 1 flooded the chain's franchises around the country and  was countered with "kiss-ins" by same-sex couples at assorted locations Aug. 3.

On its website, the Family Research Council founded in 1983, says it advocates "faith, family and freedom in public policy and public opinion" and other issues. It lobbies against gay rights, abortion and embryonic stem cell research.

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

Thirty-four gay rights groups issued a joint statement condemning the shooting:

"We were saddened to hear news of the shooting this morning at the offices of the Family Research Council. Our hearts go out to the shooting victim, his family, and his co-workers. The motivation and circumstances behind today's tragedy are still unknown, but regardless of what emerges as the reason for this shooting, we utterly reject and condemn such violence. We wish for a swift and complete recovery for the victim of this terrible incident."

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."

This story includes reporting by NBC News' Andrew Mach and The Associated Press.

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