Dr. Charles S. Dehaan’s specialty was house calls. Building his practice around patients too old or infirm to go to a doctor’s office for routine care, Dehaan for years traveled to see them at home and in assisted-living facilities across the northwest suburbs and Rockford area.

It was a lucrative business: From 2009 to 2014, Dehaan billed Medicaid alone for a total of $22 million, records show.

It also provided ample opportunity to prey on patients, according to federal and state prosecutors, police in two counties and a string of patients suing him, who say the former Des Plaines physician sexually assaulted vulnerable women with little capacity to rebuff his advances.

Dehaan, 62, has been charged with sexually assaulting four female patients in Cook County and Winnebago County, including a wheelchair-bound 80-year-old. In one case, Cook County prosecutors have charged Dehaan with repeatedly sexually assaulting a bedridden 60-year-old Des Plaines woman over a span of four years.

Before the sexual assault cases go to trial, Dehaan is due in federal court Wednesday in Rockford, where he faces a possible 10-year prison sentence after pleading guilty to Medicare fraud.

Dehaan was charged with 23 counts of Medicare fraud. But, in a deal with prosecutors, he pleaded guilty in March to just two of the charges — one for billing for a house call to a man who said he never saw Dehaan and another for a bill for seeing a patient who was already dead for months at the time of the supposed visit.

RELATED: Patients testify against Rockford doctor Charles Dehaan

Prosecutors plan to offer evidence at his sentencing that, for years, Dehaan billed Medicaid for appointments during which he sexually assaulted patients.

They’re also seeking to recover millions of dollars they say Dehaan fraudulently billed the government for.

Dehaan, who has pleaded “not guilty” to all of the sex charges, who would not talk with a reporter after a court hearing Tuesday in Skokie or over the weekend at his home in Belvidere. He denies molesting any patients, according to Debra Schafer, one of his lawyers.

“He did not sexually assault any of his patients, and he intends to vigorously defend the charges,” Schafer said.

Dehaan is charged in the four cases with aggravated criminal sexual assault and aggravated criminal sexual abuse. He’s also facing 12 lawsuits filed by patients who say he assaulted them.

The oldest of the women who say he assaulted them was 84.

“He’s a predator is what he is,” said Judith Kohl, 57, of Rockford, who’s among the women suing Dehaan.

Judith Kohl on the front porch of a nursing home in Rockford. | Andrew Grimm / Sun-Times

Judith Kohl, on the front porch of a nursing home in Rockford, is  suing Dr. Charles Dehaan, accusing him of molesting her during a house call. | Andrew Grimm / Sun-Times

Kohl said she was homebound because of a congenital bone disorder when Dehaan first saw her in 2013 and helped her get a motorized wheelchair. She said Dehaan told her during that first visit to her apartment she was beautiful and began molesting her.

“He said he was attracted to all women, whether they were disabled or not,” Kohl said. “I’m not used to having all these compliments. The next thing, he’s whipping his privates out and rubbing them all over my arms, my hands.”

In police reports filed by other women, the accusations against followed a similar pattern: compliments and come-ons followed by groping or more. In two cases, records show the patients told police they had intercourse with Dehaan. In one case, a 69-year-old woman said he squeezed her breasts and buttocks while fitting her for a wheelchair “and said something like he wanted to make sure they fit in the chair.”

Records show patients started complaining as early as 2009 to the police and state authorities.

The Department of Professional Regulation, now seeking to ban Dehaan from practicing medicine, didn’t take action against him until January 2014, when it temporarily suspended his medical license shortly before his federal indictment.

A spokesman for the state agency said the “citizen complaint” that led to Dehaan having his license suspended was filed in November 2013.

The first sexual assault case filed against Dehaan was filed in 2014 in Cook County after the Des Plaines woman saw news reports about his license being suspended and called the police, according to state’s attorney’s spokeswoman Sally Daly.

Dehaan was charged last year with assaulting three female patients in Winnebago County. According to Rockford police reports, detectives first brought two of those cases to the Winnebago County state’s attorney’s office in 2011, but it initially declined to file charges.

In one of the cases in which Dehaan is charged, a 70-year-old, wheelchair-bound woman could not identify Dehaan in a photo lineup. In another Rockford case that resulted in charges, the 69-year-old woman who said Dehaan groped her during the wheelchair fitting picked him out in a photo lineup and said, “That’s the son of a bitch.”

Winnebago County State’s Attorney’s spokeswoman Katie Zimmerman wouldn’t comment on Dehaan.

In all, 10 police reports filed with the Rockford police involved claims of sexual assault by Dehaan between 2009 and 2013, when his license was suspended.

Asked whether complaints were passed on to state regulators, Kimberly R. Bruce, a Rockford police spokeswoman, said, “In general, it is the department’s practice and policy to notify the appropriate state regulatory agencies.”

Michael Gravlin, a Chicago lawyer who represents 11 women who have sued Dehaan in Cook County circuit court for medical malpractice, said one complicating factor is that some women who complained they were victimized might not be good witnesses because of age, severe illness or mental infirmity.

“He was a home-care doctor,” Gravlin said. “To qualify for a visit from him, by definition, you have to be in pretty bad health. They’re vulnerable. They’re lonely. They depend on him for medications.”

Tim Freiberg, a Rockford attorney, represents a mentally disabled woman who has accused Dehaan in a malpractice suit of assaulting her multiple times during visits to her home in Rockford. When Dehaan’s license was suspended, the woman saw a new doctor, who, at her first appointment, diagnosed breast cancer that required a double mastectomy, Freiberg said.

“It’s something that, if he had been doing his job, he would have caught right away,” Frieberg said.

“She basically has the mentality, the ability, of a 10-year-old,” he said, “and he is making her do these things and telling her he’s going to cut off her medications or cancel her Social Security payments if she tells anyone.”

Dehaan is also facing criminal charges in that case.

“He took advantage of the elderly or mentally handicapped individuals who were not likely to turn him in, or, if they did, were unlikely to be believed,” Freiberg said. “And that’s how he was able to get away with it for so long.”