A Long Island, New York, teenager with a history of psychiatric problems killed his 15-year-old brother and brutally beat his mother – a respected physician – into a coma over the weekend, police say.

Charles Okonkwo Jr., 18, has been charged with assault on his mother, Chinwe Okonkwo, 52, Saturday in Dix Hill, New York, but does not yet face charges on the death of Bradley Okonkwo.

Mrs Okonkwo was airlifted to a nearby hospital, where she remains in critical condition. She suffered facial fractures and doctors have had to relieve swelling on her brain.

Medical examiners could not immediately determine Bradley Okonkwo’s cause of death and are doing more tests to try to determine how he died.

Charles Okonkwo Jr. was arrested Saturday night shortly after the attack was discovered. He had fled the family home in his parents’ BMW X5 SUV, but was spotted by police just a short distance away from the crime scene.

He admitted to ‘hurting’ his mother and little brother, authorities say.

In court on Sunday, a defense said that Charles Okonkwo Jr. had a history of mental illness, but didn’t elaborate on what sorts of problems he has.

Authorities also offered no motive for the alleged attack.

Members of Long Island’s Nigerian immigrant community stopped by the Okonkwo house on Sunday to pay their respects to the family.

‘This is very tragic. No one saw it coming,’ family friend Lawrence Monwe told Newsday.

‘This was the perfect family you wouldn’t expect it to happen to.’