38-year-old Justin Fields, from Alabama in the US, removed the head and at least one limb of 52-year-old Tammy Bailey on October 21, 2022.
He was caught on police body camera footage the following day at the crime scene confessing to the act.
Mark Moon, the Blount County Sheriff, said Fields had been living with his girlfriend Tammy when he killed her.
They had shared a property on Bailey Drive in Blount County but are said to have had separate bedrooms.
Sheriff Mark Moon said of the killing: “My deputies have all said it is the worst thing they have seen in their career.”
He claims the pair had recently celebrated Field’s birthday and after they got home the killer had wanted to have sex with her.
Police think an initial stab was the cause of Tammy’s death.
Sheriff Moon said: “He wanted to have sex with her. He went to her room and propositioned her and she turned him down.
“According to his statement, that frustrated him. He said he stabbed her one time and then he blacked out.”
Mr Moon told the station they believe she died after the Friday night attack, but that wasn’t the last attack on Bailey.
“On Saturday, he went back in there and felt like he was having a bad dream,” said the sheriff.
He then added that “for some reason” Fields stabbed her multiple times again.
Fields allegedly then told his father over the phone that he had done something bad.
His father told the victim’s sister and she turned up with cops but Fields wouldn’t let them in.
Moon said: “The offender grabbed her and wouldn’t let her in the house.
“He told her that he had done something horrible and she didn’t need to go in there.
“The offender tells him, on the body cam, that I have done something bad, there’s evidence in the house, and if you go in, then you’ll see it’s bad.”
He said the victim was dead at the scene.
Moon said: “It was so bad. It was over 100 stab wounds, but there’s no way to tell how many.”
Fields is being charged with murder and the abuse of a corpse.