BANGOR – A Bangor man facing charges for seriously injuring his infant son was sentenced Tuesday in Penobscot County Superior Court for supplying the weapon used in a stabbing last year.

Mathew L. Williams, 23, was sentenced to 15 years in prison with all but six suspended for providing the knife and being with Aaron Heath, 18, of Bangor when Heath stabbed a then-16-year-old boy at an Essex Street apartment building.

Heath was sentenced in October in Penobscot County Superior Court to 20 years in prison with all but 10 years suspended after pleading guilty to attempted murder.

Williams pleaded guilty earlier this year to elevated aggravated assault for his part in the incident.

He faced up to 30 years in prison for being involved in the stabbing.

Williams pleaded not guilty in November to charges of aggravated assault related to his son’s injuries. He allegedly shook the baby so violently that he caused permanent brain damage.

A trial date in that case has not been set.

Born on Aug. 18, 2005, in Bangor, the infant was 6 weeks old when he suffered irreversible brain damage. Four days after the boy was injured, a district court judge granted the Department of Health and Human Services’ request for a do-not-resuscitate order when the judge gave custody of the child to the agency.

The boy now is in foster care.

Williams and his wife Heather Williams, 21, of Bangor, opposed the DNR order.

Earlier this month, the Maine Supreme Judicial Court ruled that the child’s parents have the right to appear at a hearing to oppose such a DNR order before it is granted. A DNR order is not now in effect.

If the child dies, Williams could be charged with manslaughter, according to Michael Roberts, deputy district attorney for Penobscot County.

Heather Williams has not been charged with causing her son’s injuries.

If Williams is convicted of injuring his son, it would be up to a judge to decide if he would serve that sentence concurrently or consecutively to his sentences for unrelated crimes.

Williams was ordered Tuesday to begin serving his six-year sentence for the stabbing after he completes the two-year sentence he is currently serving for violation of conditions of release and violation of bail conditions for previous crimes.

The stabbing victim, who has recovered, lost a kidney and suffered a liver laceration as a result of the attack.

Heath admitted stabbing the 16-year-old in the abdomen as he shook the boy’s hand while Williams stood by as Heath’s backup, Roberts said.

“I’m sentencing you to 15 years in prison with all but six suspended,” Superior Court Justice Allen Hunter said in sentencing Williams. “Anything less would diminish the gravity of the crime here.”

Heather Williams, who did not address the court, covered her face with her hands and wept as her husband was sentenced.

Hunter also sentenced Mathew Williams to four years of probation after his release from prison and ordered him to pay $20,000 in restitution along with Heath to cover the victim’s medical expenses.

Roberts said after the hearing that he was pleased that Hunter had imposed the sentence his office had recommended.

Carolyn Adams of Bangor, Williams’ attorney, had asked the court to impose a six-year sentence with all but three years suspended because Williams had cooperated with police and identified Heath as the assailant.