The mom said she went to get them candy and returned to find him stabbing the little girl in the back.
A nine-year-old boy in Florida has been charged with the attempted murder of his five-year-old sister.
Ocala Police Department claimed the child tried to stab his sibling to death when their mother stepped out for ten minutes.
The little girl suffered multiple knife wounds and was airlifted to hospital.
She survived the initial attack, and was alert and responsive, but investigators have not yet provided an update on her condition, WESH reported.
The children's mother told police she had left the pair alone for a few minutes to check the mail, and to get some candy from a neighbor for them.
She said that when she returned, she walked in on the boy stabbing the girl in the back multiple times with a kitchen knife, shouting "die! die!"
The mom managed to grab the knife from him and he fled. He was later found hiding in a maintenance shed.
When detectives asked him why he did it, he said he wanted to kill her and the thought had entered his head two days earlier; he said he tried to get the thought out of his head but couldn't.
The boy is being charged with attempted first-degree murder.
At his initial court appearance on Tuesday, a judge ordered him to undergo a psychiatric evaluation, and to remain in secured detention until his next court hearing on February 5.