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.