TORONTO -- An Illinois doctor admitted in a suicide note that he went against parents’ wishes and may not have vaccinated their children, local police said.

In response, Cook County health officials issued a notice to the former patients of the late pediatrician Dr. Van Koinis, according to WGN-TV in Chicago.

His note reportedly mentioned how he felt “horrible regrets” over the way he’d handled cases in the past decade, Cook County Sheriff Tom Dart told the outlet.

Police suggested he may have forged vaccination documents to trick unsuspecting parents.

It’s unclear just how many patients were affected because Koinis’ records were incomplete and in disarray. The Chicago Sun-Times reported he had had a licence to practice medicine since 1991 and mostly dealt with patients in Chicago’s southwest side.

Sheriff Dart told the newspaper he had been “tortured” by the case of the doctor, whose note stated he had been “averse” to vaccinations and “regretted his conduct with immunizations.”

The Cook County Sheriff’s Office also stated former patients are strongly encouraged to consult their current physicians to see if all their prior vaccinations were actually conducted.

In a statement to WGN-TV, OSF HealthCare, the health-care network associated with Koinis' practice, stated he had been an “independent physician at a private practice” and that they would fully cooperate with law enforcement if contacted.

For the past several months, police have been investigating Koinis, who died on Sept. 10 from a self-inflicted gunshot wound.

The anti-vaccination movement was sparked by the now-debunked and widely discredited article that falsely and baselessly suggested immunizations were somehow linked autism in children. The Lancet, which published the article, later retracted the piece which sparked the anti-vax movement in Canada and the United States.