From Carol Cratty, CNN
WASHINGTON (CNN) - The suspect in the shooting at the Family Research Council walked into the headquarters of the conservative group armed with a 9mm pistol and shot a security guard, saying "I don't like your politics," authorities alleged in a criminal complaint filed Thursday.
The complaint accuses Floyd Lee Corkins II, 28, of a federal firearms violation and assault with intent to kill.
The council is a Christian group focused on family and anti-abortion issues and religious liberties that recently came out in support of Chick-fil-A President Dan Cathy. The executive enraged gay rights advocates when he expressed support for traditional marriage.
Corkins -- who was carrying 15 Chick-fil-A sandwiches in his backpack along with the pistol and extra ammunition -- "has strong opinions with respect to those he believes do not treat homosexuals in a fair manner," authorities said in the complaint, citing his parents.
He will be formally charged Thursday with one count of transporting weapons and ammunition across state lines, a federal violation, and one count of assault with the intent to kill while armed.
The assault charge is a District of Columbia offense that carries a maximum 30-year sentence. The federal firearms charge carries a 10-year maximum sentence.
Corkins is scheduled to appear in court on the charges Thursday afternoon in U.S. District Court in Washington, the Justice Department said in a statement.
According to the complaint, Corkins left the Herndon, Virginia, home he shares with his parents about 9 a.m. Wednesday morning and boarded Washington's subway system bound for the research council's offices in Washington.
According to the complaint, Corkins walked up to the front door of the council's office, where he encountered Johnson.
Corkins then said "I don't like your politics," or something similar, the complaint said, citing a witness.
Surveillance video shows Corkins interact with security guard Leo Johnson, then pull the 9 mm Sig Sauer pistol from his backpack and point it at him, according to the complaint. He then opened fire on Johnson, according to the complaint, hitting him in the arm.
Johnson then wrestled the weapon away from Corkins, according to authorities.
In an interview with CNN affiliate WJLA, Johnson offered a slightly different account, saying Corkins told him he was there to interview for an internship, then shot him without warning.
Johnson said it was after he had wrestled Corkins to the ground that the suspect told him the shooting was about the group's policies, according to WJLA.
While D.C. Police Chief Cathy Lanier and others have hailed Johnson as a hero, WJLA reported the 46-year-old told the station in a telephone interview that he was simply doing his job and is not comfortable being described as a hero.
Johnson's mother, Virginia Johnson, told the station her son is always trying to help people.
"I think it's wonderful, wonderful," she said of his actions.
Corkins told investigators he acted alone, according to the complaint.
Authorities who arrested Corkins recovered his pistol, two additional loaded magazines and a 50-round box of ammunition from his backpack. They found what appeared to be an open gun box on the seat of his car, which had been parked at the East Falls Church Metro station, according to the complaint.
Corkins legally purchased the handgun from a gun shop in Virginia within the last week, according to a law enforcement official.
Corkins had volunteered at the DC Center for the LGBT Community, a source working with the center told CNN. The group provides services and support to lesbian, gay, bisexual and transgender people,
He received a master's degree from George Mason University's College of Education and Human Development in 2006, the university said.
David Mariner, executive director of the DC Center, released a statement Wednesday night saying he was "shocked to hear that someone who has volunteered with the DC Center could be the cause of such a tragic act of violence.
"No matter the circumstances, we condemn such violence in the strongest terms possible. We hope for a full and speedy recovery for the victim and our thoughts are with him and his family," Mariner said in the statement.
Family Research Council President Tony Perkins said Wednesday that "our first concern is with our colleague."
White House spokesman Jay Carney said President Barack Obama was "very concerned" about Johnson, who is hospitalized in Washington.
Carney declined to say whether the White House considers the attack a hate crime, but said Obama "firmly believes that violence of that kind has no place in our society."
Presumptive Republican presidential nominee Mitt Romney used nearly identical language in decrying the attack on Wednesday.
"There is no place for such violence in our society," he said in a statement. "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."
The National Organization for Marriage, which has actively campaigned against same-sex marriage efforts, also condemned what it termed an attack on the Family Research Council.
"Everything points to the fact that this was politically motivated, and it's totally unacceptable," National Organization for Marriage President Brian Brown said in a Thursday appearance on CNN.
Brown called out the hate-tracking group Southern Poverty Law Center for listing the Family Research Council on its website, saying it was equating the group with violent extremist groups.
"The responsibility is on the shooter, but we need to have a civil debate over issues like redefining marriage," he said. "But we should not be attacking and labeling as hate groups those that we disagree. We should condemn violence of any sort, but we should also be responsible."
The SPLC says the Family Research Council defames gays and tries to make the case that the LGBT community is a threat to American society.
The council says it promotes "faith, family and freedom in public policy and public opinion."
Brown said groups such as his are boosting security after the shooting.
CNN's Greg Seaby, Javi Morgado, Paul Courson, Sandra Endo, Mike M. Ahlers and Dan Gilgoff contributed to this report.