Treyvius Turnstall, 22, pleaded not guilty to the August 12 attack that happened on the first floor inside the sporting good store in Patchogue.
Surveillance video captured the viscous attack, as a customer stabbed a store manager in a black shirt repeatedly behind the shelves.
At one point, the suspect starts to walk away, then turns back and keeps stabbing him.
The manager tried to use a ladder as a barricade, according to investigators. The disturbing attack was unprovoked.
"I believe the manager asked him if there's anything he could help him with and then without provocation, or further comment without any comment, he just began attacking him," Suffolk County District Attorney Raymond Tierney said.
Tierney says the viscous attack happened after Turnstall first entered a different Dick's Sporting Goods in Bayshore.
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Detectives say Turnstall is seen on camera buying the same machete, later used in the attack in Patchogue, a knife and a backpack.
The district attorney says Turnstall also tried to buy a rifle, but was told there wasn't any there, but that he could buy it in Patchogue.
Surveillance video captured him arriving inside the Patchogue store.
Detectives say he gave his ID to a worker behind the counter, and then Turnstall snapped, stabbing the store manager.
"He struck the manager numerous times in the head, neck, and wrist, causing him to fall on the floor," Tierney said. "While the victim was on the floor, Turnstall continued to his attack with the machete and continued to hit him with the weapon."
What appeared to be the store manager, bandaged up on both arms, attended Turnstall's arraignment.
The district attorney says the manager has a fractured skull and wrist and has tendon and nerve damage in both hands.
The manager wasn't alone. Investigators say Turnstall slashed two customers, one before running out and the other in the parking lot, before running away.
Suffolk County Police caught Turnstall nearby. They also found the machete.
Turnstall was charged with attempted murder and assault. It carries a maximum sentence of 25 years.
Turnstall's bail was set at $1 million in cash and $2 million bond.
He has one prior, a misdemeanor.
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