An Adelaide court has heard gruesome details of a man's three-day drug-fuelled crime spree in which he held an autistic man captive and dismembered his own housemate's dog.

Key points: Rech committed the crimes while on bail for assaulting police in September 2017

Rech committed the crimes while on bail for assaulting police in September 2017 He was in a "drug-affected haze" when he held a man captive then killed a dog the next day

He was in a "drug-affected haze" when he held a man captive then killed a dog the next day He will be sentenced next week on Friday January 25

James Alexander Rech committed the "sadistic" crimes last July while he was on bail for assaulting police in September 2017.

In sentencing submissions, Rech's defence lawyer Stephen Ey told Judge Sophie David that the 20-year-old was addicted to the drug ice, prescription medication and alcohol, and his use of these had "escalated" in the lead-up to his crimes.

The court heard that on July 6 last year, Rech made threats to a man who he did not know.

The defence told the court Rech was in the middle of a "three-day methamphetamine binge" when he held a separate autistic man captive at his Hampstead Gardens home on July 9.

Mr Ey said his client was in a "drug affected haze" when "he lost it" and stabbed his victim before using a blowtorch and a knife to cauterise the wounds.

Prosecutor Georgina Venn told the court Rech mocked his victim when he moaned in pain.

"The defendant laughed at him and told him he found that noise funny," Ms Venn said.

Plastering debt leads to dog's death

The court heard Rech's drug-fuelled crime spree continued the following day.

On July 10, police found him walking along the busy North East Road carrying the dead dog's head and a meat cleaver while covered in blood, after neighbours reported a disturbance at his nearby home.

"One can't fathom what he was thinking," Mr Ey told the court.

"He's gone outside, wandering around, holding it [the dog's severed head] up," Mr Ey said.

"It beggars belief."

The court was told Rech was in remission from leukaemia. ( ABC News: Eugene Boisvert )

RSPCA prosecutor Damon Ind told the court bloody paw prints were found at the scene.

"The dog was trying to escape," he said.

Mr Ind said Rech stabbed the Staffordshire bull terrier more than 20 times before dismembering the animal, severing its head, legs and tail.

"It's an extremely cruel, painful way for that dog to die," he said.

The court also heard Rech had told his housemate — named only as "Fry" — three days earlier that he would kill the dog if he did not pay his parents back for plastering work that had been done to fix a hole in a wall.

Mr Ind said that proved Rech had committed the crime with intent.

Both Mr Ind and the police prosecutor told the court Rech's offending was serious and urged Judge David to reflect that in his sentence, which will be handed down next Friday January 25.

Victim 'changed forever' from attack

The court also heard victim impact statements from the autistic man and his mother and sister, which were read out by the prosecution.

"I keep seeing an orange knife held up against my skin … [Rech] heated a knife with a blowtorch, then cauterised me," the man wrote.

"[It was] the most pain I have felt in my life.

"He treated me like I was a stain on his dirty floor."

Ms Venn said Rech held the victim captive for three hours and made him clean his kitchen.

The man escaped and texted his mother, who described the ordeal in her victim impact statement.

She said her son's life and the life of her family "had changed forever" after Rech's "sadistic behaviour".

"The stench in my car is something I'll never forget … blood and burning skin," her statement said.

"You not only stabbed my child, you cauterised him."

20yo defendant in remission from leukaemia

The defence urged the judge to take into account Rech's "significant medical issues" while deliberating on his sentence.

The 20-year-old's lawyer said he was in remission from leukaemia and had hip and knee issues that were akin to that of "an advanced elderly person" that had required "multiple surgeries".

Mr Ey said his client was supposed to see his oncologist monthly but that had "not happened as regularly since being in custody".