Bob, a 42-pound tortoise, was slashed and stabbed after being taken from the California home of a six-year-old autistic boy.
Police said the attacker tried to cut Bob out of his shell.
His hind legs were badly cut, a toe was cut off, his neck was slashed and his shell was punctured.
Jose “Tony” Mosqueda, 18, was arrested in connection with cruelty to animals and theft charges.
Sergeant Jack Richards said: “It’s a good feeling. It just really pulled at some heartstrings, and it’s good to have someone in custody.”
Witnesses to the torture provided information that helped lead to the arrest, Richards said.
The 25-year-old tortoise is a special friend to Dorothy and Bill Sullivan’s autistic son, who rarely spoke to people but chatted to the animal.
The tortoise was snatched from their garden in Ventura on July 7, brutalised and dumped in brush behind an apartment complex. An anonymous caller told the family where to find him.
Police declined to discuss a motive, but Richards said it did not appear the attacker wanted to eat Bob.
The tortoise was being treated at Turtle Dreams, a rehabilitation centre. He was being fed through a tube in his neck.
“He’s getting more relaxed and coming out of his shell” more often, said Jeanie Vaughan, the centre’s owner. “If he continues without any infection, I think he’s going to be fine.”