A Colorado customer stopped to get a quick bite from Taco Bell only to become violently sick. The burrito he ingested contained rat poison.

Authorities responded to a report of a disturbance at Taco Bell on Smoky Hill Road in Centennial, a city south of Denver, around 1 p.m. on January 15. When Arapahoe County Sheriff deputies arrived, they were informed that an intense argument had broken out between employees and a customer.

According to the Taco Bell manager, Lary Swift, the customer “wanted something free” because there was a problem with the drink station. She added that he frequented the restaurant often, and it was not the first time that his exchanges with staff had become heated.

The customer had been given an extra burrito, and he then went on his way.

Hours later, a nearby hospital contacted the Sheriff’s Office to inform them that a patient was being treated for having ingested rat poison.

After speaking with the victim, investigators learned that he was the same customer from the Taco Bell disturbance reported earlier. He had come home, worked around the house, watched TV, and then proceeded to eat his food. After becoming violently ill, he called 911 and was transported to the hospital.

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According to the Sheriff’s Office, rat poison was found in the remainder of the man’s food.

When authorities returned to Taco Bell, Swift denied that this was possible, since they did not even carry rat poison.

“We didn’t do anything like that. It didn’t even add up. It’s ridiculous,” Swift said to CBS News.

Nonetheless, as Sheriff Deputy John Bartmann told reporters, the department has opened an investigation into the matter and is calling it a “criminal attempt homicide” due to the harm it could have caused to the man.

Investigators are reviewing all surveillance footage from inside and outside the restaurant.

“Right now what we’re looking at is if the rat poison was actually put into his food at the restaurant. We don’t know if it was, at this point in time,” Bartmann told CBS News.

Taco Bell is cooperating with investigators, and its corporate office released a statement:

“The safety of customers and team members is a priority. The franchise who owns and operates this location has informed us that they are working with local authorities in their investigation.”

While the Taco Bell restaurant had been closed by the authorities on Sunday, it was reopened after county authorities performed a health inspection and it passed.

The man, whose identity is unknown, was released from the hospital.