Court records say the accused scientist told police resentment toward a co-worker had built for years.
MADISON, Wis. — A University of Wisconsin-Madison scientist accused of poisoning a co-worker’s belongings told police he had grown angry after the colleague received a second promotion that he did not get, court records say.
The allegation against Makoto Kuroda, 41, is being handled as both a criminal case and a campus workplace matter. Prosecutors charged him April 14 with second-degree recklessly endangering safety and tampering with household products. UW-Madison said Kuroda, a staff scientist at the Influenza Research Institute in the School of Veterinary Medicine, is on administrative leave and has lost access to university labs, digital systems and research privileges while officials investigate.
The complaint paints the case as a workplace conflict that moved from resentment into an alleged chemical attack. Police said Kuroda and the co-worker, identified only as TM, met at the institute in 2017 and once were good friends. Kuroda told officers that both men had been promoted, but TM later got another promotion while he did not. After that, Kuroda said, he believed TM began acting as if he were better than him. He described TM as disrespectful and said TM treated supervisors better than subordinates.
Kuroda also gave police a set of smaller complaints that he said had built over time. He said TM failed to wear a lab coat when supervisors were away, ignored a meeting about lab coats and did not follow rules about goggles. He also described what he called an unwritten rule about waiting before crossing a center hallway in the labs. Kuroda said TM crossed in front of him as if he were not there and threw trash into a bin in a way that made a loud noise. The complaint says Kuroda felt the act was intentional.
TM gave police a different view of the workplace. He told officers he did not have issues with anyone and did not know how a chemical could have gotten into his water bottle. He said he would feel safer if his office door locked. When police later spoke to him again, TM said he and Kuroda had once been close but he was unsure how they drifted apart. He also described a prior episode in a downstairs locker room in October, when clothes he had left outside a locker were moved and laid out on a table. TM said he felt creeped out, though the complaint does not say Kuroda admitted that event.
The alleged poisoning began with a water bottle and shoes left in TM’s office. According to the complaint, TM opened a new plastic water bottle from Trader Joe’s on April 2 and drank part of it. He left the bottle on his desk. On April 4, he noticed a strange odor and chemical taste when he drank from it. He spat out the water, dumped the rest and kept the bottle. On April 6, he noticed the same odor in his office and traced it to lab shoes he kept under a table. Those shoes stayed at the institute and were not taken home.
Another employee, AK, told police she smelled the bottle and noticed something was off. AK said the shoes also smelled of a chemical and felt the matter should be reported. Police were called that day, and the Madison Fire Department Hazardous Incident Team helped collect the bottle April 7. Preliminary testing at the Wisconsin State Laboratory of Hygiene detected chloroform in water residue. The complaint says the level was so high that test strips could not give an accurate value and that investigators found the result concerning because chloroform fades over time.
Police said Kuroda admitted what happened April 10. TM told Officer Adrian Vera that Kuroda came up to him in the lab and said, “I did it,” then commented on the shoes. TM said he felt scared and left the area. A supervisor, identified as YK, said Kuroda sent an email in Japanese after YK notified staff about the incident and police involvement. The translated email said, “I did it. I have also informed the person himself. I am very sorry.” YK also told police that Kuroda admitted in person that he put paraformaldehyde in TM’s drink.
During a police interview, Kuroda allegedly described how he used the chemicals. He said he arrived at work April 5 around 8 a.m., left around noon and returned in the evening to continue culturing bacteria. He saw TM’s half-full bottle on the desk, went back to the lab and used a syringe to retrieve paraformaldehyde mixed with Trizol from his own work refrigerator. Police said he reported putting about 0.5 milliliters of 4% paraformaldehyde in the bottle and a mixture of Trizol and 4% paraformaldehyde in each shoe.
Kuroda told police he expected the co-worker to get sick, according to the complaint. He said even a small amount of paraformaldehyde could cause irritation and a rash in the mouth and throat. He expected stomachache, vomiting and dizziness if TM drank the water, police wrote. He also said the shoe mixture could cause rash and discomfort, though he believed socks would reduce the effect. “My aim was just, he feel bad,” he told police, according to the complaint. Police said he later acknowledged that he should not have done it.
The complaint says Kuroda was familiar with the chemicals. He told police he had used paraformaldehyde since he started at the job about eight years earlier and knew it well enough to pick an amount intended to make someone sick but not kill him. He also said about 10 milliliters of paraformaldehyde would be a critical or lethal dose. Police said Kuroda still had the vials of paraformaldehyde and Trizol in his refrigerator after the incident. He also told officers he had unrestricted access to those substances.
UW-Madison said the final chemical analysis was pending, but the criminal complaint and university statement named paraformaldehyde, chloroform and Trizol as the alleged substances. The university said those chemicals are common in research laboratories and said the case was not tied to the institute’s research materials. The Influenza Research Institute studies viruses that cause illnesses such as flu and COVID-19. UW-Madison said the institute is subject to major safety and security measures and that staff must pass federal security risk assessments connected to the Federal Select Agent Program.
The case also raises questions about access and documentation. A witness told police that chloroform was available in the main lab and annex lab, that everyone at the institute had access during the day and that the chemical was locked after everyone left. The same witness said there were no cameras covering where chloroform was stored or used and no records for its use. UW-Madison said the institute provides frequent training so lab members know and follow protocols, including wearing personal protective equipment.
Kuroda was arrested April 10 and booked into the Dane County Jail. The Dane County Sheriff’s Office later listed him as a pretrial resident at the Public Safety Building, with the case number 2026CF000839. Court records cited in public reports say bond was set at $5,000 and that Kuroda was ordered not to contact TM and not to enter UW-Madison laboratories. The university said it cannot release more information because of employee privacy laws and the pending criminal case.
The next steps include court proceedings, further lab analysis and the university’s workplace investigation. Police have said the incident appears isolated and that there is no known threat to public safety, but they also said the investigation remains open and additional charges may be filed.
Author note: Last updated 2026-05-06.