A gun store in Aurora, Colo., in 2013 (Ed Andrieski/AP)

The first time Benjamin Bishop walked into Lock N Load and tried to buy a gun, employees at the Florida gun store turned him away — and rightly so.

Bishop had been diagnosed with schizophrenia and claimed he was attacked by assailants — who existed only in his imagination, court records say. He abused bath salts, which intensified the hallucinations, and he punched holes in walls with a hammer and claimed he was Osama bin Laden, the documents say. After his mother had him involuntarily committed, he tried to strangle her.

State and federal laws were designed to keep guns out of the hands of people like Bishop, but he wanted one anyway.

So the second time he went to Lock N Load in Oldsmar, Fla., he brought a neighborhood acquaintance. As Bishop stood nearby, the 18-year-old acquaintance bought a 12-gauge shotgun for $279 in cash, court documents say.

The transaction was a straw purchase, in which someone buys a gun for a person who is legally prohibited from possessing one. Straw purchases are illegal for both the buyer and the seller, though the Tampa Bay Times reported that the teen who bought the shotgun later cooperated with authorities and wasn’t charged with a crime.

Outside the store, the neighbor turned the 12-gauge over to Bishop, who said he wanted to use it to protect himself from gang members.

NoneBenjamin Bishop in 2014. (Pinellas County Sheriff’s Office)

But Bishop used the weapon on his mother instead: In 2012, he shot Imari Shibata and her boyfriend as they slept in their home in Pinellas County. She’d told him that he needed to get a job and that he had to take his schizophrenia medication. Bishop was furious.

“I was, like, in a rage,” he later told the Tampa Bay Times. “I was throwing doors down and stuff. I was cussing out my mom’s boyfriend. I was mad at my mom because she was forcing me on medication. She said either that or I was going to get kicked out of the house.”

He fired eight rounds at the couple, then called 911 to confess. Bishop’s mom and her boyfriend, Kelley Allen, were found dead at the scene.

Bishop, now in his early 20s, is serving two consecutive life sentences in prison. With the gunman off the streets, the families of the victims and the Brady Center to Prevent Gun Violence focused their attention on Lock N Load, the store where Bishop got his gun.

A lawsuit filed in 2014 in a Florida circuit court by the families and the Brady Center claimed that the store’s owner, Gerald Tanso, didn’t do enough to keep a dangerous weapon out of the hands of a mentally ill man with a criminal record.

The parties settled. Most of the details of the settlement are confidential, but one part was made public: Tanso agreed to sell his gun store and never sell a firearm again.

Tanso has never been charged with a crime in Bishop’s case, nor were any of Lock N Load’s employees.

But if anyone “was personally and acutely aware of the risk associated with supplying firearms to mentally unstable individuals,” the lawsuit says, it should have been Tanso.

In 2011, his store sold a .38-caliber pistol to Julie Schenecker, who cleared all the appropriate checks, then used the gun to kill her two children. She’s serving two concurrent life sentences in prison.

Tanso initially called the legal action a “bogus lawsuit” filed by people who “are looking for money,” according to the Tampa Bay Times.

But on Friday, as part of a settlement, he released a statement via the Brady Center that encouraged gun owners to be cautious about whom they sell to.

“I have sold my gun shop and will no longer engage in the business of selling firearms,” Tanso said in the statement. “Our Second Amendment protects the rights of law abiding citizens and we must protect those rights. At the same time, we must exercise great caution and due diligence with great responsibility in preventing firearms from getting in the wrong hands of people who seek to harm us all.

“I support laws that protect our Second Amendment and the laws that protect our society from criminal elements who would abuse that right to the detriment of others. I encourage all gun dealers, including the new owner of my gun shop, to implement such measures.”

The statement listed several measures that go beyond what the law requires, including asking questions to ensure gun buyers aren’t purchasing them for prohibited people and maintaining and reviewing records of trace requests.

Attorneys for the plaintiffs told The Washington Post that other conditions of the settlement were confidential.

A man who answered the phone at a home phone number listed for Tanso said the former gun store owner was on vacation. Tanso did not return a message.

Jonathan Lowy, a Brady Center attorney involved in the case, said the organization has been going after the small percentage of gun stores that, he said, are responsible for 90 percent of the guns used in crimes.

“Most gun dealers are responsible business people who do what they can to prevent dangerous people from getting guns, but unfortunately there are some that don’t,” Lowy told The Post.

“For those gun dealers who just care about the bottom line and just care about the money they make from the next gun sale … lawsuits like this mean it’s no longer profitable. … We’re hoping we can change the calculus for those gun dealers.”

Last year, the Brady Center, a nonprofit that advocates for gun control and against gun violence, settled a $2.2 million wrongful-death lawsuit with a Missouri gun dealer who sold a gun to a mentally ill woman who then killed her father, according to the Kansas City Star.

Gun-control advocates had a number of other successes recently, according to The Post’s Amber Phillips: Twenty state legislatures rejected bills to allow guns in public without a permit. Seventeen states rejected bills to allow guns in schools. And Hawaii and Washington passed laws requiring that police be notified when a felon or domestic abuser tries to buy a gun and fails a background check.

But 60 bills supported by the National Rifle Association also became law this year, Phillips reported, and West Virginia, Tennessee and Arkansas reduced gun-free zones in public buildings and parks.

Marion Hammer, a former president of the NRA who is now a lobbyist for the organization, said it doesn’t comment specifically on lawsuits it is not involved in, but she criticized the Brady Center’s tactics in general.

The Brady Center “is determined to find any way it can to destroy Second Amendment rights of citizens,” she said, adding: “There don’t appear to be individuals they target — it’s a cause. And if they get an individual gun shop owner in their sights, they’re going to spend whatever it takes unless the courts step in and put a stop to this malicious behavior.”

The Brady Center was founded as the National Council to Control Handguns in 1974. In 1981, it was renamed after James Brady, President Ronald Reagan’s press secretary, who was permanently disabled during the 1981 assassination attempt on Reagan. Brady and his wife became strong voices for gun control, fighting for legislation that would require background checks to buy a gun from licensed firearms dealers. Brady died in 2014.

Despite the Brady Center’s victories in Florida and Kansas City, Erich Pratt, executive director of Gun Owners of America, said courts have been throwing out similar cases for years.

“It’s wrong to punish the seller of a legal product for doing what’s constitutionally protected,” he said in an interview. “The bad guy in this case is the murderer. You don’t go after Chrysler because a car that was sold by a dealer is used to run somebody over.”

But Lowy said the Brady Center goes after “bad-apple gun dealers” who skirt laws enacted to keep guns out of the hands of dangerous people.

Lock N Load still exists, but it has a new owner: Dominic Zingale, a federally licensed firearms dealer, who said in a written statement to the Tampa Bay Times that he “will continue to follow all of the applicable ATF, Florida, and local guns laws and procedures set forth by them to the letter.” He added that he has “no operational ties to the former owner nor have I worked with him when he was in the firearms business.”

“Honestly, I don’t think they should,” he told the Tampa Bay Times. “Guns are pretty fun to shoot.”

But the Times said Bishop also referenced the 2012 massacre in Newtown, Conn., in which Adam Lanza fatally shot 20 children and six staff members at Sandy Hook Elementary School.

“I don’t know,” he said in 2013. “Just don’t give to somebody who’s going to end up killing a bunch of innocent 6-year-olds.”