A criminal complaint says investigators traced a tainted bottle and shoes to a workplace dispute inside a campus research institute.
MADISON, Wis. — A report of an unusual odor inside a University of Wisconsin-Madison research office led police to charge a staff scientist who they say admitted using lab chemicals to poison a co-worker’s water bottle and shoes.
The case against Makoto Kuroda, 41, moved quickly from a campus safety call to a felony prosecution. Police first received a report of chemicals in an employee’s belongings April 6. A hazardous materials team collected evidence April 7. By April 10, police said, Kuroda had confessed. Prosecutors filed two felony counts April 14, and the university removed his access to its labs, systems and research privileges while it conducts its own review.
The alleged victim, identified only as TM in court records, had not expected a criminal investigation when the odor first appeared. According to the complaint, he opened a plastic water bottle April 2, drank about half of it and left it open on his desk at the Influenza Research Institute. On April 4, at about 2:30 p.m., he returned to the office and noticed a bad smell. He took a drink, tasted something chemical and spat it out. He dumped the rest of the water but kept the bottle. Two days later, he traced the same smell to shoes he kept at work.
Another employee, identified as AK, helped move the matter toward police. The complaint says AK was asked to smell the bottle and noticed that it was off. AK also said TM’s shoes smelled of a chemical. TM did not want to make a big deal of it, but AK felt it should be reported, according to the complaint. Officer Brock Prough was sent to the institute, located in the 500 block of Science Drive, at about 1:13 p.m. April 6. TM told police he did not know how the substance got into the bottle and initially had no idea who could have done it.
Police then began treating the water bottle and shoes as evidence. TM told officers the bottle stayed in his office the whole time and that the shoes were under his table. He said he wore the shoes in the lab but did not take them home. A second employee, identified as PH, smelled both items and said the odor seemed like Trizol or chloroform. PH told investigators chloroform was available in the institute’s lab and annex lab, unlocked during the day and locked after people left. PH also said there were no cameras on the storage area and no use records for the chemical.
The Madison Fire Department Hazardous Incident Team arrived April 7 at about 2:30 p.m. to help collect the bottle and send it to the Wisconsin State Laboratory of Hygiene. The complaint says the team swept the area where the items had been kept overnight and reported no chemical concerns, though fire officials said their meters could not detect chloroform. At about 4:45 p.m., Officer Prough received preliminary results. Residue in the water bottle was presumptively positive for chloroform, and the level was so high that test strips could not provide an accurate value.
The investigation changed again three days later. Officer Adrian Vera responded April 10 to a report that a staff member had admitted poisoning another employee’s drink. AK identified the employee as Kuroda. TM then told Vera that Kuroda had approached him in the lab, said, “I did it,” and made a comment about the shoes. TM said the remark scared him and he left the area. A supervisor, YK, told police Kuroda had also admitted the act in person and in an email written in Japanese. A translated version quoted in the complaint said, “I did it. I have also informed the person himself. I am very sorry.”
Kuroda spoke with police after receiving Miranda warnings, according to the complaint. He said he understood his rights and agreed to answer questions. Police wrote that he described years of tension with TM, who had been his friend after they met at work in 2017. Both men worked at the institute for their postdoctoral research, and both had been promoted. Kuroda told police TM received another promotion while he did not, and he said TM then acted as if he were better than him and treated subordinates poorly.
The complaint describes a list of grievances that police said Kuroda gave during the interview. He said TM did not follow lab rules about wearing a coat and goggles when supervisors were gone. He described an unwritten hallway rule that he believed TM ignored. He also said TM threw trash in a way that made a loud noise and felt intentionally disrespectful. Kuroda told police the stress grew until it made him “do this.” Police said no blatant threats had been reported before the incident, though TM also described a past episode involving clothes moved from a locker room area.
Kuroda said he returned to work April 5 in the evening and saw TM’s half-full bottle on the desk, the complaint says. He told police he went to the lab, used a syringe to retrieve paraformaldehyde mixed with Trizol from his own work refrigerator and placed some into the bottle and shoes. The complaint quotes him saying he used about 0.5 milliliters of 4% paraformaldehyde in the bottle and a mixture of Trizol and 4% paraformaldehyde in each shoe. He said he discarded the syringes, returned the vials to his refrigerator and left around 6:15 p.m.
Police also wrote that Kuroda researched harmful amounts before the incident. The complaint says he used ChatGPT on his work laptop to look up harmful amounts of paraformaldehyde and Trizol for humans and animals. It says the program gave him warning pop-ups about what he was asking, but Kuroda told police he did not reconsider. He allegedly said he wanted TM to feel sick, not die. He expected stomachache, vomiting, dizziness, rash or discomfort, according to the complaint.
UW-Madison said the chemicals alleged in the case were paraformaldehyde, chloroform and Trizol, all routine laboratory supply chemicals. The university said final analysis from the Wisconsin State Laboratory of Hygiene was still pending. It also said the episode was unrelated to the research conducted at the Influenza Research Institute. Scientists there study viruses that cause illnesses such as flu and COVID-19. UW-Madison said it had already contacted the FBI after the arrest because employees at the institute are subject to security screening under the Federal Select Agent Program.
The criminal case now carries two counts. Prosecutors charged Kuroda with second-degree recklessly endangering safety, a Class G felony, and tampering with household products, a Class H felony. The complaint says the tampering count involves an allegation that a household product was tainted with intent to kill, injure or otherwise endanger health or business and that the act created a high probability of great bodily harm. A conviction on both charges could bring a combined maximum sentence of 16 years in prison and $35,000 in fines.
The university said Kuroda is on administrative leave and that his physical and digital access to university assets has been revoked. His research privileges also have been revoked. UW-Madison police said after the arrest that the incident appeared isolated and that there was no known threat to public safety. Police also said the investigation remained ongoing and that more charges could be filed. Public jail records listed Kuroda as a pretrial resident at the Dane County Public Safety Building after his arrest.
Kuroda’s case remains pending in Dane County Circuit Court, where court filings and laboratory testing are expected to shape the next stage. The university’s workplace investigation is also continuing, and UW-Madison said privacy laws and criminal proceedings limit further comment.
Author note: Last updated 2026-05-06.