ALFRED, Maine (AP) — A man who was angry because his grandmother asked him to move out of her home was convicted Friday of killing her by beating her, stabbing her dozens of times and setting her body on fire.

Jurors found Derek Poulin guilty of murder and arson in the death of 61-year-old Patricia Noel, who was beaten with a golf club and stabbed about 70 times before the home they shared in Old Orchard Beach was set afire. He faces a minimum of 25 years in prison for murder and up to 40 years in prison for arson when he’s sentenced at a later date.

Investigators found no conclusive fingerprints or DNA on the murder weapons after the intense fire in October 2012. But prosecutors said there was plenty of circumstantial evidence pointing to Noel’s grandson, whom Assistant Attorney General Donald Macomber described as an “unemployed, unmotivated pot smoker.”

Defense lawyer Amy Fairfield had told jurors the real killer was free because investigators focused all their attention on the wrong man and never considered as a suspect Poulin’s father, who they said had blood on his running shoes.

Prosecutors said they had the right man and noted that strong circumstantial evidence pointed to Poulin. They said his alibi didn’t match with receipts found in his car and the clothes he turned over to police didn’t match with camera footage from that day.

Fairfield also pointed out that the 26-year-old Poulin has long suffered from mental illness. The defendant was committed to a state psychiatric hospital last year for an evaluation, and the judge ruled him competent to stand trial a day before opening statements were delivered.