A former University of South Florida doctoral student was caught on a hidden camera injecting toxins he mixed at the campus' chemistry lab into his neighbors' apartment, sickening their newborn, according to court records.

Xuming Li, 36, was arrested June 27 after Umar Abdullah captured him on surveillance video on two separate occasions crouching next to his front door and using a syringe to squirt a mixture of deadly toxins into his home, according to a complaint.

"How could someone be so callous?" Abdullah told Fox News Digital in a statement. "The incident still haunts us like the worst nightmare."

For more than a year, Li had complained about noise from the Tampa, Florida, apartment above him after Abdullah moved in with his wife in June 2022.

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Xuming Li show with syringe in surveillance footage next portrait of Abdullah family

Umar Abdullah, his wife, Samira, and their infant daughter were sickened after Xuming Li allegedly injected poison into their Tampa, Florida, apartment. (Umar Abdullah | Facebook)

The couple welcomed a little girl two months later.

Li, who was working toward his Ph.D. in chemistry, said he was kept up at night by heavy footsteps, the dragging of furniture and a creaky toilet seat.

Abdullah said his family did everything they could to accommodate Li but nothing worked and tensions continued to flare. Li called the police on his neighbors in March, complaining about the noise and reported the family to the homeowners' association, records show.

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Beginning in early June, the conflict took a disturbing turn.

The Abdullahs began noticing a noxious odor and suffered alarming symptoms, including headaches, dizziness and stinging eyes.

"To my shock, my daughter's eyes and nose were filled with tears, and she was vigorously scratching her eyes while coughing," Abdullah said. His daughter refused to eat and had bouts of vomiting.

Xumong Li shown crouching down with a syringe.

This video screenshot allegedly shows ex-chemistry student Xuming Li injecting opioids under his neighbor's door over a noise dispute. (Umar Abdullah)

They suspected freon may have leaked from their AC unit, but a mechanic found nothing wrong. They also worried that gas might be escaping from their water heater, and their landlord replaced it.

But the troubling symptoms persisted. Abdullah noticed on June 25 that the smell was worse near the front door and concluded that "someone was deliberately" poisoning his family.

He installed a small camera outside the door concealed in a plant. The next morning, on June 26, his daughter erupted into a fit of coughs and vomited.

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Abdullah checked the camera and saw that two minutes before his daughter became ill, Li allegedly had bent down in front of their door and then quickly hurried away.

But Abdullah needed better footage. He adjusted the camera and waited.

In the early evening of June 27, Li allegedly struck again, but this time Abdullah had crystal-clear video and called police.

A headshot of Umar Abdullah next to a screenshot of Xumong Li holding a syringe outside his door.

Umar Abdullah, left, and Xuming Li, who is charged with injecting deadly opioids under the door of Abdullah's apartment. (LinkedIn | Umar Abdullah)

A hazardous materials team determined that the noxious substance was a concoction of the opioids methadone and hydrocodone, the complaint says.

A police officer and Tampa firefighters who came into contact with the mixture broke out in rashes from the toxins, according to a police report.

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"The mixture was extremely hazardous and life-threatening," Abdullah told Fox News Digital. "Inhaling the poison could lead to rapid entry of toxins into the bloodstream, which posed an even greater risk for babies."

Their daughter was treated at an emergency room.

"Seeing her tiny hand with an intravenous catheter, enduring those painful pokes and tests, tore me apart inside," Abdullah said.

Xumong Li stares stonefaced wearing an orange jumpsuit

Xuming Li (Hillsborough County Sheriff's Office)

The building's homeowners association filed a breach of contract lawsuit against Li, who owns his apartment, to try to boot him from the complex. 

Abdullah has also filed a civil suit against Li, who is facing seven counts of burglary, aggravated stalking and other charges.

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His lawyer, Adam Bantner, declined to comment. Li was released on bond and is due back in court in December.

The University of South Florida said Li didn't return to the school after the summer of 2023.