On August 9, 2012, France TV briefly interviewed Floyd Lee Corkins II for a general story on buying guns at a store in Chantilly, Va. This occurred the week before the shooting of an unarmed security guard last summer at the D.C. headquarters of the conservative Family Research Council. Corkins pleaded guilty in federal court on Wednesday to the shooting. (The Washington Post)

The shooter of an unarmed security guard at the Family Research Council headquarters last summer was on a mission to target organizations he viewed as anti-gay, and he obtained a gun days before he tried to carry out a plan to kill “as many people as possible,” according to newly disclosed court documents.

New details about Floyd Lee Corkins II emerged Wednesday in federal court, where he admitted to the politically motivated shooting at the conservative think tank in downtown Washington. Corkins, 28, pleaded guilty to three felony charges: a federal charge of transporting a firearm and ammunition across state lines and D.C. charges of assault with intent to kill and committing an act of terrorism while armed.

In the days before the shooting on Aug. 15, Corkins purchased a semiautomatic pistol, had it modified to be “more effective” and received training at a shooting range, court documents show. He drew up a list of four conservative groups and loaded a backpack with a 9mm SIG Sauer pistol, two magazine clips and 50 rounds of ammunition.

“Were it not for the heroic guard who tackled Floyd Corkins, he could have succeeded in perpetrating a mass killing spree in the nation’s capital,” U.S. Attorney Ronald Machen said in a statement. “This case highlights the dangers of access to high-capacity magazines that allow killers to inflict carnage on a mass scale in the blink of an eye.”

The accounting of Corkins’s access to a firearm comes against the backdrop of a national debate over gun control prompted by the mass shooting at an elementary school in Newtown, Conn., in December. Corkins purchased his weapon legally in Virginia, a gun-rights state where no major new firearms restrictions are under consideration in Newtown’s aftermath. A state law enacted after the massacre at Virginia Tech in 2007 prohibits firearm sales to people deemed by a judge to be mentally “defective,” but Corkins had no criminal record.

Less clear is whether post-Newtown proposals elsewhere would have blocked Corkins’s purchase. In Maryland, Gov. Martin O’Malley (D) has proposed a broad package of restrictions, but he stopped short of proposing a measure like Virginia’s regarding the mentally ill.

Corkins, who told the judge Wednesday that he is taking medication and being treated for “severe depression,” was so angry at the anti-gay-marriage positions of the Family Research Council and the fast-food chain Chick-fil-A that he devised a scheme involving both.

Corkins, who had volunteered at a gay community center in Northwest, told FBI agents that his goal was to target people opposed to same-sex marriage and “smother Chick-fil-A sandwiches in their faces,” according to a plea agreement he signed in December. He had bought 15 Chick-fil-A sandwiches the day before, an apparent symbol of his antipathy for the head of the fast-food chain, who had recently spoken out against same-sex marriage.

A detail sure to reignite the culture wars that erupted around the shooting is the fact that Corkins told FBI agents that he identified the Family Research Council as anti-gay on the Web site of the Southern Poverty Law Center. The day after the shooting, Tony Perkins, the president of the Family Research Council, suggested that the center’s labeling of the organization as a hate group had given Corkins a “license to perpetrate this act of violence.” On Wednesday, Perkins said the revelation had validated his earlier comments.

A spokeswoman for the center said the group never listed the address for the Family Research Council on its Web site. The law center has said that Perkins’s group deserves the label because of its claim, for instance, that pedophilia is a “homosexual problem.”

At the time of the shooting, conservative commentators also accused media outlets of giving the shooting less coverage than other gun crimes because the perpetrator was a liberal. Those accusations resurfaced Wednesday.

The court documents show how Corkins methodically tried to carry out his plan. For years, he told FBI agents, he had been thinking about “perpetrating similar violence.” “He initially wanted to make a bomb, but did not have the patience to do it.”

Raw video: Family Research Council shooting suspect Floyd Corkins is arrested in August 2012. (The Washington Post)

Six days before the shooting, Corkins purchased the pistol from Blue Ridge Arsenal in Chantilly. While there, the French television station France 2 happened to interview Corkins as he held and pointed the pistol as part of a story on how easily firearms can be bought in the United States.

On the day of the shooting, Corkins told the security guard he had an interview for an intern position. When Johnson asked for identification, he pulled a gun out of his backpack.

Corkins fired three times, striking Johnson in the left forearm. Within seconds, Johnson wrestled Corkins to the ground and took his weapon. Johnson spent about a week in the hospital, where he had two metal plates put in his arm to allow the bones to heal.

At the scene, police said they overheard Corkins saying, “I don’t like these people, and I don’t like what they stand for.”

U.S. District Judge Richard W. Roberts told Corkins that he could face up to 30 years in prison on each of the two local charges and up to 10 years on the federal charge. His sentencing is scheduled for April 29.