BOSTON — FBI agents say they caught a Hyde Park man running at dawn with a loaded pistol in his waistband — and ended the morning by ripping an entire war chest of weapons out of his apartment.

The feds didn’t just stumble on Kenneth Bigby-Williams by accident. This was the payoff to a “lengthy and thorough” probe by the FBI Metro Boston Gang Task Force and Boston Police’s District E-5 Drug Control Unit.

Just before 6 a.m. on Thursday, August 7, investigators say Bigby-Williams stepped out of 142 Margaretta Drive and headed toward Georgetown Drive. When they moved in and told him to show his hands, he allegedly took off — clutching his waistband like a man who really didn’t want to lose what was inside it.

He didn’t get far. After a quick sprint, agents had him face down, pulling a loaded Ruger 5.7 from his waistband — a sleek, high-velocity pistol straight out of a cartel playbook — plus a 20-round magazine and spare ammo.

Then came the home search. Inside the apartment, investigators say they uncovered enough firepower to turn a quiet Hyde Park block into a war zone:

• Smith & Wesson M&P-15 assault-style rifle
• Glock 43 (9mm)
• Glock 22 (.40 caliber)
• Sig Sauer P250 (.45 caliber)
• Hundreds of rounds of assorted ammo
• High-capacity magazines, including a 28-round Glock mag and a 40-round rifle mag
• Gear from rifle cases to speed loaders

One charge on the list? Improperly storing a rifle or shotgun near a minor — a detail that’s sure to raise eyebrows about just who was around all this hardware.

Bigby-Williams now faces a rap sheet that reads like a gun control activist’s nightmare: unlawful carry of a firearm (second offense), unlawful possession of an assault weapon, three counts of unlawful possession of a firearm without an FID card, and more.

The FBI hasn’t said whether these guns are tied to other crimes — but in a city already on edge over violence, the discovery of a Hyde Park arsenal before breakfast is the kind of story that sticks.