BALTIMORE – A 14-year-old boy has been charged as an adult with attempted murder after police said he beat his 66-year-old grandmother with a hammer until she became unconscious.

Hassanhii Garrett has been charged with attempted first-degree and attempted second-degree murder, first- and second-degree assault, reckless endangerment and use of a dangerous weapon, police Detective Kevin Brown said Friday.

Investigators said the incident happened at about 8:30 a.m. Thursday at a home in the 800 block of East 34th Street.

A police spokeswoman said the beating happened as Garrett was getting ready for school and that the boy called 911 after the assault.

The woman, identified as Shirley Garrett, was unresponsive in an upstairs bedroom of the home and was suffering from several head injuries when authorities found her, police said. She was taken to an area hospital, where she is listed in critical condition.

Hassanhii is at Central Booking. He told police that he was angry about the way his grandmother had been treating him, 11 News learned.

Police charging documents said the boy got the hammer from a second-floor bathroom, then walked into his grandmother’s bedroom, raised the hammer and struck her on the head while she was sleeping.

The police document said the teen continued to beat his grandmother with the hammer and his fists after she woke up. The teen told police the attack continued after his grandmother stumbled and fell.

Police said they found obvious signs of a struggle.

Hassanhii has no known history of trouble that juvenile authorities or police knew of, 11 News I-Team lead investigative reporter Jayne Miller said. According to court records and family members, Shirley Garrett fought for custody of him when his mother died in 2002.

The boy was a public speaker in 2005 at the groundbreaking of a community playground, Miller reported.

Stay with and WBAL-TV 11 News for updates on this story.