(CNN) When William Forsyth retired after decades as a county prosecutor, the Battaglia family thanked him for convicting their son's killer -- 25 years after his murder.

"With the resolution of the case, Bill has given us the gift of healing," Joel Battaglia's mother, Gail, recalled saying before she embraced Forsyth at his retirement dinner in 2016

Now, Forsyth, 68, finds himself at the helm of a high-profile case likely to demand the same persistent push for justice -- and looming promise of healing -- as he steps in as the special prosecutor investigating how former Michigan State University physician Larry Nassar could have sexually abused girls and young women for nearly 20 years without the school intervening.

In 40 years as a prosecutor -- 30 of them as the top elected lawyer in Kent County, Michigan -- Forsyth tried more than 40 murder cases and oversaw thousands of others. Christopher Becker, who worked for Forsyth before succeeding him, said his former boss always made clear that lying to him or to the court or withholding evidence would get them fired.

Other attorneys praised Forsyth's appointment in the Michigan State matter, calling him meticulous, detailed, fair, compassionate and genuinely concerned about crime victims.

"He's going to look for the truth," Becker said. "I think that drives him."

'Seeking justice'

Rachael Denhollander and Kyle Stephens, two survivors of Larry Nassar's abuse, and others embrace at his sentencing.

In a speech last week, Forsyth talked pointedly about his search for the truth during his career -- and now.

"I've always believed as a prosecutor that probably the most important function as a prosecutor is to represent the victims of crime. And in each case, I've always tried to view it as ... seeking justice, searching for the truth and doing the right thing," he told reporters. "And that philosophy has pretty much guided me in my entire career. And it's the philosophy that I'll bring to this investigation."

A Michigan judge last week sentenced Nassar to 40 to 175 years in prison after he pleaded guilty to seven counts of criminal sexual conduct in Ingham County, and admitted to using his trusted medical position to assault and molest girls under the guise of medical treatment.

More than 150 girls and women asserted during Nassar's sentencing hearing this month that he sexually abused them under the guise of medical care as a Michigan State or USA Gymnastics physician over two decades.

Now, Forsyth will lead an investigation into the school itself that began last year, according to Michigan attorney general Bill Schuette, who announced the investigation after Nassar was sentenced. Shortly after the sentencing, Michigan State President Lou Anna Simon and Athletics Director Mark Hollis also announced they would step down.

Nassar had already been sentenced to 60 years in prison for federal child pornography charges and had pleaded guilty to three charges of criminal sexual conduct in Eaton County, Michigan. He is scheduled to be sentenced Wednesday on those charges.

Forsyth acknowledged the complexity and scope of the investigation, which he said would be painstaking.

"Everybody, I'm sure, would like to get this done and wrapped up as quickly as possible, while quick is a relative term depending on the context in which you're using it," he told reporters last week. "And to quote legendary UCLA basketball coach John Wooden, 'We're going to be quick, but we're not going to hurry.' We're going to do a thorough job, and we're going to do this the right way."

"But you have to bear with us and remember what it is we're being asked to look at," he added. "This is almost 20 years of predatory conduct on the part of Nassar."

"And when we're done, I can't promise that everybody's going to be satisfied with our report and what we find," he said. "But I can promise you that we're going to work extremely hard at our task, and you will get our best effort."

'A very youthful 68-year-old'

When Forsyth retired, he couldn't stay retired.

"He's has to do something. He's a very youthful 68-year-old," said his daughter, Andrea Forsyth, an attorney in Grand Rapids.

For several months, he returned to Kent County to help the staff prepare for the resentencing of several juveniles convicted of murder and sentenced to life without parole. The work included one case he'd tried: the conviction of Federico Cruz, who killed a teenager and recorded himself talking to the severed head, Becker said.

Cruz, who was sentenced in 1997, and many other then-juvenile offenders faced resentencing in light of a US Supreme Court ruling that mandatory life sentences without parole for juveniles amount to cruel and usual punishment, CNN affiliate WXMI reported.

The juvenile cases are pending while the Michigan Supreme Court decides whether a jury or a judge should decide the sentences, Becker said.

More recently, when the chief of the two-person prosecution team in William Forsyth's small hometown of Standish, Michigan, said he needed an assistant, Forsyth agreed to come on board, his daughter said.

A grandfather, Forsyth has always stayed active, she said. He often ran during his lunch break when he was prosecutor. Andrea Forsyth and her father enjoy going mountain climbing together and recently scaled Mount Rainer in Washington state and Mount Whitney in California, she said.

'A model independent prosecutor'

William Forsyth was doing chores around the house when Schuette -- who described the retired prosecutor as "a man of immense integrity" with "an impeccable reputation" -- called to ask him to be the special prosecutor in the Michigan State investigation, his daughter said.

The job was perfect for her father, she said.

"He's meticulous," she said. "He doesn't have an agenda. He's not motivated by anything but getting to the bottom of it, getting to the truth."

Photos: Olympic gymnasts who have accused Larry Nassar of abuse Reigning Olympic all-around champion Simone Biles said in mid-January, on the eve of Larry Nassar's sentencing, that she was one of the many girls and young women who was sexually abused by the former USA Gymnastics team doctor. "There are many reasons that I have been reluctant to share my story," she said, "but I know now that it is not my fault." Hide Caption 1 of 4 Photos: Olympic gymnasts who have accused Larry Nassar of abuse Aly Raisman, a three-time Olympic gold medalist, confronted Larry Nassar in court: "Larry, you do realize now that we, this group of women you so heartlessly abused over such a long period of time, are now a force, and you are nothing," she said. "... I will not rest until every single last trace of your influence is on this sport has been destroyed, like the cancer it is." Hide Caption 2 of 4 Photos: Olympic gymnasts who have accused Larry Nassar of abuse 2012 Olympic all-around champion Gabby Douglas said she was also abused by Nassar. "I didn't publicly share my experiences as well as many other things because for years we were conditioned to stay silent and honestly some things were extremely painful," she posted on Instagram.

Hide Caption 3 of 4 Photos: Olympic gymnasts who have accused Larry Nassar of abuse Two-time Olympic medalist McKayla Maroney said Larry Nassar molested her repeatedly, starting when she was 13 years old. "It happened in London before my team and I won the gold medal, and it happened before I won my silver," Maroney tweeted. Hide Caption 4 of 4

Kevin Bramble, an assistant prosecutor in Kent County, recalled Forsyth working so hard on the Cruz case that he looked drawn out in the face.

"He really poured his heart and soul into it," Bramble said. "He's one of the guys that is just so thorough and doesn't leave any stone unturned."

Forsyth was an early proponent of victim advocate programs in Michigan and helped start one at the Kent County Prosecutor's Office, Becker said.

Advocates assist victims through the legal process and many times read their victim impact statements to the court.

"If you could build a model independent prosecutor, he would be it," said Vicki Seidl, a prosecutor in Kent County. "You would want somebody with his charter, with his sense of right and wrong and his sense of responsibility, his sense of fairness."

Battaglia said she witnessed Forsyth's compassion when her son's killer was sentenced. Tears welled up in his eyes during the proceeding, she said.

"He was with us in our pain and our sorrow," she said, "but also our joy."

Corrections: Earlier versions of this story incorrectly spelled the names of Vicki Seidl and Eaton County. The story also has been updated to correct a quote from Forsyth's daughter.