EVERGREEN PARK, Ill. (CBS) — Investigators are digging into the records of a southwest suburban pediatrician who took his own life.

There are concerns about whether the vaccinations of some of Dr. Van Koinis’ young patients were fake.

CBS 2’s Jim Williams reported Tuesday from the late doctor’s office in Evergreen Park.

Dr. Koinis worked out of a building on West 95th Street in Evergreen Park. The office was locked Tuesday, five months after he took his own life.

Investigators found a suicide note raising questions about his vaccination records.

It was last September when Koinis was found dead from a self-inflicted gun shot wound.

The Cook County Sheriff’s office said his suicide note indicates there might be a problem with records he kept regarding the vaccinations children received, or did not receive, at his office on West 95th Street in Evergreen Park.

“The note was very short. It was a note where he expressed a lot regret and the note was solely driven at the fact that he did things he regretted as far as the vaccinations,” said Cook County Sheriff Tom Dart. He added Koinis also expressed regret in doctoring records.

“He was incredibly regretful for what he did and it was the only thing he mentioned in the suicide note. It was this and only this,” Dart said.

Dart said that the note mentioned a window spanning about 10 years in which he either doctored records or gave fake vaccinations. Koinis was a big believer in homeopathic remedies. The note didn’t express regret in those beliefs but “regrets in what he did.”

Dart said that from a preliminary investigation, Koinis didn’t have financial problems or problems with his practice. But the suicide note detailing his vaccination practices gives him pause.

“Our thinking is that would mean that people who came there came with a purpose to get records phonied up, not have to take the vaccine and take the records to a school that would allow their child to be admitted even though their child never had a vaccine.”

As a result, the Cook County Sheriff’s office said confusion over the records is making it difficult to determine what children received vaccinations.

“It was a little bit cryptic but in some places, very straightforward in the conduct that he was regretting,” Dart said, who noted the vaccine situation was connected to his suicide.

“There seems to be an overarching depression that was driven by years of not vaccinating people properly. We were not able to nail it down any further,” Dart said. “That was the sole reason he gave for this.”

It was those clues that led his office to investigate the doctor, his records and other connections to his practice. He was a solo practitioner and didn’t work with any other doctor.

“He was an individual who practiced homeopathic medicine and was very much into holistic medicine and apparently a lot of individuals who are against vaccinations were attracted to him,” Dart added.

Investigators found the possibility that in some cases Dr. Koinis did not provide vaccinations at their parents request.

“Was this just the case where individuals who were against vaccinations came to him. He waived vaccinations and phonied up records or is this larger than that,” questioned Dart.

“We feel that there was people who came to him purposely to get the sign-off on vaccinations that they did not get,” Dart said, who added that those people who got a phony sign-off could face criminal charges, including forgery.

Tatiana Rudolph brought her two children to Dr. Koinis and she said both received their shots.

“He never hesitated to give vaccinations. He never hesitated at all,” Rudolph said. “If they needed them for school, they were getting them.”

Records indicated Koinis began practicing his medical career in 1991. People in the same office building told CBS 2, off camera, that he was quiet and at times odd.

Rudolph said he was a good doctor.

“Doctor Koinis was a very caring loving doctor,” she said. “He was very observant. He paid close attention. He did his best with everything.”

Some other parents were also quick to defend Dr. Koinis.

“He was the absolute best physician, honestly. When I first had my daughter, we went into our first appointment and I was terrified as a new mom and he made it a point to check not only on my daughter, but on me constantly,” said Dana Hamed, who has one child. “He would randomly text me and say hey, how’s Lilly doing? How are you guys doing? How are you keeping up on being a new mom? And I was absolutely blown away because I would have never in a million years imagined a doctor to do that.”

Hamed said she did not believe the claims about Koinis’ conduct.

“I’m upset because what is being said is not true and I’m in communication with a lot of his patients, as well as his nurses and they told me it’s not true. Everybody I’ve talked to has told me that,” she said. “Their kids are up to date on their vaccinations. Their kids received their vaccinations in front of them, as did I and it was proved in the emergency room that my daughter was up to date on her vaccinations.

But another parent, Mary Mullaney, said she’d had doubts about Koinis’ methods.

“My oldest son now is 13, and when we went for his 12-year vaccinations, something was going on with him. He was just very different. He wasn’t the same doctor that I had been taking my kids to,” Mullaney said.

She continued: “He had always been stuck on like the technology aspect of technology ruining children’s brains, but this visit, I mean I sat there for about 45 minutes and he kept going on and on and on. I was just there for the checkup and he actually ended up telling me that my son didn’t need the vaccines that the school had said, so I believed him and then my son’s school actually contacted me saying if he didn’t have these shots that he wouldn’t be able to come back, so when I went back to Dr. Koinis, he was kind of surprised. We got the shots. He gave it to him. I hope that’s what he gave him.”

Mullaney said she went back another time when her son became sick.

“Dr. Koinis kept telling me oh, it’s a virus, it’s a virus, but I knew something was wrong. I kept asking him to send us to a specialist or something and he wouldn’t. He told me it wasn’t necessary. He went back on the technology stuff,” she said. “So I actually ended up pulling my kids from the practice and found out my son actually ended up having like life-threatening food allergies.”

Dart said there’s no concrete evidence that he was actively misrepresenting to people that he was vaccinating when he wasn’t.

“But the substance of the note he left was very broad and very specific about vaccination issues and records being faked.” Dart said. “This seems to be almost exclusively at vaccinations  He had probably 2,500 patients.”

Dart said there is a test called the titer test that can determine whether or not an individual has had certain vaccinations. The parents of Doctor Koinis’ young patients are urged to the call the Cook County Sheriff’s Office if they have any concerns.

Authorities they also suggest calling a child’s current doctor.