Before he died, Van Koinis, an Illinois pediatrician, wrote of his regrets about immunizations. The authorities are now investigating whether he had been misleading patients.

Investigators are looking into which of Dr. Van Koinis’s patients did and did not receive vaccinations.Credit…LM Otero/Associated Press

An Illinois pediatrician’s mysterious suicide note has raised troubling questions about the immunization records of children in the Chicago-area community he served for years.

The doctor, Van Koinis, had been missing since August when he was found dead of a self-inflicted gunshot wound on Sept. 10 in a forest preserve in Palos Township, the authorities said.

Investigators said they had found an “unusual” and “dark” suicide note at the scene in which Dr. Koinis expressed “horrible regrets” regarding immunizations over the past 10 years, prompting an investigation into which of his patients received vaccinations and which did not, the Cook County sheriff, Thomas J. Dart, said on Friday.

“In the course of his note, he just made it sound like this was haunting him for a long time,” Sheriff Dart said.

A statement from the Cook County Sheriff’s Office said investigators had obtained information that suggested that in some cases, Dr. Koinis “did not provide vaccinations to children at their parents’ request.”

“Was he just doing this pursuant to patients’ requests and then lying about the records, where these kids get into schools where you’re required to have immunizations?” Sheriff Dart asked. “Or was it something where he went beyond that, where people who thought they were immunized were not getting it?”

In their investigation, the authorities had spoken with two people who had worked for Dr. Koinis, but were unable to gain clarity on the matter. After speaking with some patients, the investigators learned that Dr. Koinis, who had been licensed to practice medicine in the state since 1991, was a proponent of homeopathic medicine, Sheriff Dart said.

“He was pretty well known for that,” the sheriff said. “It wasn’t a secret.”

The physician was also popular in the Evergreen Park community where he practiced, Sheriff Dart said. Numerous reviews on Zocdoc, an online medical care appointment booking service, praised his professionalism and bedside manner.

Dr. Koinis had about 2,500 patients at the time of his death, but it was unclear how many patients he had treated over the past decade or why the doctor had a number of patients who did not live in the general area, Sheriff Dart said.

Since revealing their concerns about the suicide note, the authorities have received phone calls from people expressing worry or detailing “strange experiences” at the doctor’s office in regards to vaccinations, Sheriff Dart said.

At least a few of Dr. Koinis’s patients have come to his defense.

Tatiana Rudolph, a mother of two, told CBS Chicago that Dr. Koinis “never hesitated to give vaccinations.” Another parent, Dana Hamed, praised the doctor for constantly checking up on her and her daughter, according to the station. “I was absolutely blown away because I would have never in a million years imagined a doctor to do that,” she said.

In its statement, the sheriff’s office encouraged former patients to consult with their current physicians and “inquire about methods to test for prior vaccinations.” At least one local school district had publicly reiterated concerns from the sheriff’s office.

Melaney Arnold, a spokeswoman for the Illinois Department of Public Health, said in a statement on Friday that the agency was very concerned about the situation, noting that “vaccination is the best protection against many diseases.”

Dr. Len Horovitz, an internist and pulmonary specialist at Lenox Hill Hospital in Manhattan, said on Friday that falsifying medical records was an offense that could land a physician in trouble, especially if it concerned public health.

According to Dr. Horovitz, patients can be tested for vaccinations they may have received or may be missing. “Most vaccinations can be assessed with antibody levels — that includes chickenpox, measles, mumps, rubella” and others, he said.

Those who are not immunized should receive a booster. “It’s not only safe to do that, it’s recommended,” he said.