LAKE WALES, Fla. (AP/CBS Tampa) — Authorities say a central Florida teen killed his grandmother, who was found stabbed nearly 100 times, struck in the face with a wrench and shot in the head with a crossbow.

The Polk County Sheriff’s Office reports that 19-year-old Jasper Aristotle Smiddie was arrested Wednesday morning and charged with first-degree murder.

Authorities say Smiddie’s father contacted authorities Tuesday. The father said Smiddie had called him and confessed to killing 67-year-old Gloria Helfrich. Smiddie lived with his grandmother and uncle in a Lake Wales home, where deputies found the body.

“Here, Grandma takes you in when apparently no one cares about having you around,” Polk County Sheriff Grady Judd said at a news conference Wednesday, according to The Ledger. “And the only thing she gets is to be murdered, viciously murdered.”

Judd said that Helfrich was stabbed 93 times – 58 times in the back, 34 times in the head and once in the face. After stabbing her, he then hit her in the face with a wrench.

Smiddie told authorities he killed his grandmother to cause pain to his uncle.

“He wanted to inflict as much pain (on his uncle) as possible,” Judd said, according to The Ledger.

A friend told Polk County authorities that Smiddie originally planned on killing his uncle.

Smiddie was arrested in Highlands County after he was spotted near his girlfriend’s home.

(TM and © Copyright 2012 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2012 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)