AUGUSTA – Kenneth McDonald was sentenced Wednesday to 30 years in prison for fatally stabbing and beating his mother a year ago in the Monmouth home they shared.

At the sentencing hearing in Kennebec County Superior Court, McDonald, 44, described the events that led up to the slaying on Aug. 24, 2009, after she refused to allow him to take a vacation alone to the Maine coast.

“This happened because I wanted to prove to my mother I could do something on my own I tried to convince her. I couldn’t,” McDonald said. “I wish I could take it back.”

McDonald, who stands 5-foot-8 and weighs about 250 pounds, wore thick glasses with plastic frames heavily taped around his nose.

Reports from forensic evaluators described him as a man of low to average intelligence.

The circumstances of the attack on Janice McDonald were detailed over two days of graphic testimony at the start of the trial, which ended Sept. 1 when McDonald pleaded guilty to murder.

Under a plea agreement, McDonald was to receive a sentence of 25 to 40 years.

McDonald originally pleaded not guilty to the murder charge.

McDonald testified that he’d never gone on a date, never brought friends over and was constantly belittled and criticized.

“She’d say I was too fat. I was too stupid. I couldn’t do anything right,” McDonald said.

McDonald said he had to work up the courage to tell his mother he wanted to go alone on a trip. When she refused, they argued.

“Janice McDonald was verbally abusive toward Kenny, and eventually she slapped him,” defense attorney James Billings wrote in the defendant’s sentencing memo. “Kenny’s anger eventually boiled over due to this incident and the accumulated anger of his whole adult life of being controlled by his mother.”

Assistant Attorney General Leane Zainea said Janice McDonald, 80, “did the best she could to raise her son whom she understood had certain limitations.”

“Janice McDonald didn’t deserve to die,” Zainea said. “He went to the kitchen to pick up a knife and brutally stabbed her over and over.”

Psychologist Charles Robinson, who evaluated McDonald for the defense, wrote in a sentencing memo that McDonald reported his mother told him that, if he left, he would never come back.

“Paradoxically, Mrs. McDonald was as dependent on Kenneth for her psychological well-being as he believed himself to be dependent upon her for his very existence,” Robinson wrote. “He had been groomed since birth to maintain an infantilized state and observed to me that his mother ‘always treated me like I was 7 years old.’“