BOSTON (AP) -- Gov. Charlie Baker signed into law April 13 the most extensive overhaul of the state's criminal procedures in decades.

The new law makes changes to everything from the state's bail system to the use of solitary confinement in prison and calls for greater use of programs that divert some youthful offenders and people struggling with mental health issues or drug addiction away from involvement with the courts.

The law also will let certain prior offenses, including those no longer crimes, such as possession of small amounts of marijuana, be expunged from a person's record.

"Viewed as a whole this bill takes our criminal justice system and makes it better," Baker said.

Baker highlighted sections of the new law that would crack down on those trafficking in the synthetic opioids fentanyl and carfentanil, expand protections against witness intimidation and increase penalties for repeat operating under the influence, or OUI, offenders and for corporate manslaughter.

He also pointed to new mandatory minimum sentences for assault and battery on a police officer causing serious injury.

The law also repeals several mandatory minimum sentences for low-level drug offenses, changes the threshold for which theft is considered a larceny from $250 to $1,200 and raises the minimum age for criminal responsibility from 7 to 12.

Supporters of the law say it goes a long way toward making the justice system fairer and offers a hand up to those who have been incarcerated and are trying to get their lives back on track.

"Years and years of advocacy by community leaders, legislators and powerful black and brown grassroots organizers created a sea change in Massachusetts politics," said Democratic Sen. Sonia Chang-Diaz, of Boston. "This is a huge victory for justice and shows what we can accomplish together."

Middlesex District Attorney Marian Ryan, a Democrat, called the new law "a meaningful step forward in reforming our criminal justice system."

Ryan said she was proud that "restorative justice practices" used in Middlesex County to intervene in the lives of at-risk youths and young adults by offering a range of diversion options are expanded under the new law.

The Catholic bishops of Massachusetts sent a letter to members of the Massachusetts Criminal Justice Reform Conference Committee back in February applauding the committee's efforts in crafting criminal reform legislation. In the letter they detailed items they hoped for in the new legislation, including eliminating certain mandatory minimum sentences, creating rehabilitation and reentry programs, providing services to those suffering from mental health struggles.

The overhaul, praised by Republican and Democratic lawmakers, was approved a week earlier by votes of 37-0 in the Senate and 148-5 in the House.

Baker said the administration will seek $15 million to begin putting the new law into effect, while the total cost for the new law in the 2019 fiscal year, which begins July 1, could be $40 million.

Even as he signed the bill, he said he was filing a new criminal justice bill that would address issues in the new law.

He said one change he would like to see would give parents the option to testify against their children instead of prohibiting their testimony. He said parents should not be compelled to testify, however.

Baker also said police should continue to have access to sealed criminal record. He said that access is critical to firearms licensing decisions and the ability to properly evaluate day care workers.

Pilot staff contributed to this report.