A 69-year-old man arrested in Jacksonville, Florida, on Friday had threatened to “shoot up” a mosque, the Federal Bureau of Investigation said.

While driving to a gun range on November 10, Bernandino Bolatete told an undercover detective that he was planning to stage a mass shooting at the Islamic Cultural Center of North East Florida, according to a federal indictment. In recorded conversations, Bolatete, a Philippine national who worked at a liquor store attached to a strip club, said he hated Muslims and had an arsenal that included five rifles, one of which was an AR-15. He also made statements indicating that he had scouted possible locations from which to open fire and identified the days when worship services would be most heavily attended.

But that’s not why Bolatete was arrested on Friday. Although he could face additional charges, he is currently being held on a federal weapons-possession violation for buying a silencer from the undercover detective. On December 1, Bolatete paid $100 for the device, which would attach to his “pistolized AR,” according to the indictment. He said he didn’t want to go through the federal application process to buy a silencer because he didn’t want to open up his property to government scrutiny.

Three days before the transfer, Bolatete texted the officer: “Altho the suppressor is not really that ‘quiet’ but it can be used on the 4th of July or New Year time, it can easily blend with the sound of fireworks.”

For 83 years, silencers, also known as suppressors, have been tightly regulated by the federal government under the National Firearms Act. Obtaining one of them is considerably harder, and more costly, than buying a handgun. Applicants must pay a $200 tax, undergo a vetting process that can stretch to a year, and register their purchase with the federal government. Two bills in Congress aim to remove the devices from federal regulation, ostensibly to protect shooters’ hearing.

Opponents of the bills say that deregulation would make it easier for people with violent intentions to perpetrate shootings and evade detection. Second Amendment advocates counter that silencers are rarely used in crimes.

But that may have a lot to do with their relative scarcity. Silencers were used in all manner of heinous crimes before they were regulated by the federal government. My colleague Alex Yablon highlighted several silencer-aided murders in the pre-NFA 1920s, a run of crimes so gruesome it led the device’s inventor to abandon silencer manufacturing altogether. In fact, the pro-gun talking point around suppressors may serve only to highlight how effective the NFA has been over the decades.

Because silencers are so tightly regulated, criminals often must find creative ways to obtain them. Todd Kohlhepp, the South Carolina serial killer who confessed last year to fatally shooting seven people, allegedly bought five silencers through a straw purchaser because, as a convicted felon, he would not have passed federal muster. In July, Kenneth Gleason, 23, who was recently indicted for the random fatal shootings of two black men in Baton Rouge, Louisiana, in September, filled out an application for a silencer, but hadn’t received it yet because of the several-months vetting process.

One bill that aims to deregulate silencers is stalled in the House of Representatives, despite 164 co-sponsors. Another bill, which has just five co-sponsors, was scheduled for a hearing on the day of the shooting at a Congressional baseball practice in June, and it was scheduled for a vote the week after the Las Vegas massacre in October. There’s been no movement on it since then.