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U.S. federal agents used Urban Dictionary to bust an Indiana man accused of sending a barely comprehensible death threat on Facebook to a gun store manager, according to a U.S. District Court complaint.

Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives searched the slang decoder after Justin Kemble, 27, dim-wittedly wrote he wanted to “murk” the manager of Midwest Gun Exchange, in Mishawaka, Indiana, on the company’s profile page.

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Kemble penned the ill-judged pledge on Aug. 29 following an altercation with a store manager earlier that day. The manager, Brad Rupert, tipped off authorities that Kemble had presented a pistol with a defaced serial number and asked whether it was a problem. Law enforcement officials promptly went to the store, interviewed Kemble and seized the weapon – leading to the ominous online rants.

Following an exchange with a Facebook friend, in which Kemble complained the “ATF just took 1 of my guns”, he allegedly then wrote on the store’s Facebook page: “That 1 f– in there got my pistol confiscated, I got plenty of other guns but I want to murk that (expletive).”

Urban Dictionary defines the verb murk as: “To physically beat someone so severely, they end up dying from their injuries… To seriously whoop somebody’s a–.” To add weight to their case, prosecutors even included these definitions in the criminal case file.

Kemble, who claimed he had bought the gun from his former stepfather for $200 earlier this year, appeared in a federal courthouse on felony charges. A judge ordered him jailed ahead of a Sept. 6 detention hearing. (via The Smoking Gun)

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Joe Jackson is a contributor at TIME. Find him on Twitter at @joejackson. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.