A Florida teenager was charged Wednesday with murdering his grandmother by stabbing her 93 times and shooting her in the head with a crossbow.

Jasper Aristotle Smiddie, 19, confessed to stabbing his grandmother, 67-year-old Gloria Helfrich, shooting her in the head with a crossbow and beating her with a pipe wrench, MyFoxTampaBay.com reports.

He reportedly told investigators that he "blacked out and woke up two hours later with blood all over his hands and his grandmother," FOX 13 reports.

Authorities say Smiddie decided to kill his grandmother to make his uncle suffer. They say he originally plotted to kill his uncle, but decided to kill Helfrich instead.

"He decided, 'Well, I'll kill my grandmother instead so that my uncle has to live with the death of his mother for the rest of his life,' " Sheriff Grady Judd of the Polk County Sheriff's Department said.

Authorities say they do not know why the teen hated his uncle so vehemently, but told MyFoxTampaBay.com that he has been very open about the murder.

Police say Smiddie killed his grandmother in her bedroom in the home they shared. Then, in a bizarre twist. he locked the door and waited for his uncle to get home. The teen then ate dinner and watched television with his uncle, who had no idea his mother lay dead in her bedroom.

Smiddie left the home in the morning, then reportedly called his father in Tampa and told him what he had done. His father called the police, and directed them to the woman's body.

Smiddie was arrested near his girlfriend's home and charged with first-degree murder.

Teen charged with killing his grandmother with a crossbow: MyFoxORLANDO.com

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