Authorities have arrested and charged a man suspected of attacking an 85-year-old man at a yard sale with a hatchet.

Michael Farmer, 43, of Speedwell, was arrested Saturday by the Knox County sheriff's office on a charge of aggravated robbery stemming from an unrelated incident, said spokeswoman Martha Dooley.

Farmer is a suspect in an Aug. 14 attack in Knoxville that seriously injured Harley Tapp, according to Knoxville police Sgt. Tim Snoderly.

Farmer hasn't been charged in connection with the attack on Tapp but he has been interviewed by Knoxville police investigators, Snoderly said.

Police believe robbery was the motive for the attack. A man who came by the yard sale asked Tapp for a specific item when no other customers were around, and Tapp led him to a shed to get it.

When Tapp's back was turned, the man grabbed a hatchet and attacked him. The man ran off with some cash stolen from Tapp.

Relatives later discovered Tapp's van was missing, and police believe the attacker may have driven off in it. Tapp had surgery to repair injuries to his head and arm after the attack.