BANGOR, Maine — A Millinocket man was sentenced Tuesday at the Penobscot Judicial Center to 2½ years in prison for assaulting and threatening his grandmother in a case Penobscot County District Attorney R. Christopher Almy described as elder abuse.

Derrick J. Sirois, 29, had been held at the Penobscot County Jail unable to make $10,000 cash bail from the time of his arrest on Dec. 11 until his sentencing Tuesday. That time is expected to be credited toward his sentence.

After his sentencing, Sirois was moved to the Maine State Prison in Warren, according to jail personnel.

Sirois was drunk last year when he went with his 66-year-old grandmother to her Millinocket apartment, Almy said Thursday. Sirois demanded pills and money from the woman, as he has in the past.

When she did not comply, Sirois struck her in the chest, stomped on her foot and threatened her with a burning cigarette, according to the district attorney, who prosecuted the case. In addition, Sirois threatened to kill his grandmother if she did not give him what he wanted.

The grandson also pulled out a knife and threatened to use it if she or a witness called the police, Almy said. The grandmother tried to flee, but the defendant caught her and continued to assault her until the witness was able to call Millinocket police.

When officers arrived, Sirois was arrested and taken to jail. The grandmother was taken to a local hospital for treatment and released, according to court documents.

Between Jan. 1 and 5, 2011, Sirois called his grandmother, with whom he was forbidden to have contact, from jail, threatened her and tried to bribe her into not coming to court to testify against him, Almy said.

Just before his sentencing by District Court Judge Patrick Ende, Sirois pleaded guilty to domestic violence assault and domestic violence criminal threatening, both Class C crimes, for the December attack. He also pleaded guilty to Class B tampering with a victim and Class C violation of bail.

Sirois faced up to 10 years in prison on the Class B crime and up to five years on the Class C convictions. In addition, he faced fines of up to $10,000 and $5,000, respectively.

Almy praised the work of Millinocket police Officer Martin Legassey and Sgt. Aaron Brooker.

“They investigated the case properly and thoroughly and enabled us to get the sentence on Sirois that he deserved,” Almy said Thursday.