DUBLIN — Investigators found the powerful opiate Fentanyl at the Dublin middle school where a man died and a woman working with him on the school’s cleaning staff was hospitalized earlier this week, police said Thursday.

The two adults who worked as custodians at Fallon Middle School were reported missing Wednesday morning after not returning home after their shift Tuesday night.

When authorities arrived at the school Wednesday morning around 7 a.m., they found two people unresponsive. A 32-year-old man was pronounced dead and a 29-year-old woman was taken to the hospital for treatment. Police say she’s expected to fully recover.

Dublin Police Capt. Nate Schmidt said Thursday morning that investigators confirmed the presence of the drug, Fentanyl, at the scene. Even a small amount of the drug can be deadly, he said. Investigators have not officially ruled it a drug overdose; they are waiting on toxicology reports following the autopsy. Police do not believe it to be a murder-suicide attempt.

When officers arrived, they smelled a chemical odor. The fire department’s hazardous-materials team was called but found no obvious chemical presence or toxins in the air throughout the entire school.

Although a sealed chemistry science kit was found in the library, experts confirmed that even if it had been opened and all the chemicals mixed together, the combination would not have caused a reaction, he said.

The stepfather of the man described him as a caring father to two children.

Dublin Unified Interim Superintendent Daniel Moirao sent two messages out to parents Wednesday informing them of the man’s death.

“Our deepest sympathies go out to the family and friends of our lost colleague and also to the students, staff and community of Fallon Middle School. No matter how strong the Fallon Mustang family is, losing a family member at any time is tragic, but during this time of year, it is devastating,” Moirao said.

Initially, there was speculation online that the incident may have involved a student, which was not true.

“In situations of this nature, rumors often spread quickly, which can result in additional pain and suffering for the family and friends of those involved,” the superintendent said.

He asked the community to avoid speculation and let police do their jobs.

There were no groups of children on campus meeting at Fallon recently. The district had plans to return to in-person learning as early as Jan. 1. However, given Alameda County’s return to the most restrictive purple tier on the state’s color-coded COVID-19 classification system, reopening will not occur until the county reaches the red tier.

Although students were on winter break, Tuesday was a working day for district staff, and custodians were on campus for their regular shifts.

Staff writer George Kelly contributed to this story.