Police are investigating a New Year's Day attack in a Perth prison on murderer Trudi Lenon, who is waiting to be sentenced over the gruesome stabbing and garrotting death of autistic teenager Aaron Pajich.

The 44-year-old has been held at Bandyup Women's Prison since she and her accomplice, 26-year-old Jemma Victoria Lilley, were convicted in November of killing Mr Pajich.

About 8:00am on Monday a prisoner in the jail, on Perth's north-eastern outskirts, assaulted Lenon, leaving her with severe burns.

The Department of Justice did not name Lenon, but confirmed a prisoner had been attacked and taken to Fiona Stanley Hospital.

She remains at the hospital, where she in a stable condition receiving treatment for her wounds.

The Department has referred the incident to WA Police, with CCTV footage to be reviewed to determine who attacked Lenon.

Police said Midland Detectives were investigating the assault, which had been carried out by a single inmate.

Women obsessed with serial killers

During the five-week trial, Lilley and Lenon had employed the "cut throat" defence, trying to blame each other for killing the autistic 18-year-old.

But the Supreme Court jury took only two-and-a-half hours to find both women guilty.

Lilley had never met Mr Pajich, who had studied with Lenon at a local college, but the two women lured him to the Orelia home they shared and into a trap.

Aaron Pajich's body was recovered from under a concrete slab at the women's home. ( Supplied: Facebook )

His body was found buried under a freshly laid slab of cement that was covered in bright red tiles in the backyard of the home.

The teenager had two stab wounds to his neck and one to his chest, as well as an injury on his neck consistent with being attacked with a garrotte.

Lilley, who the court heard was obsessed with tattoos, knives, violence and serial killers, maintained she was asleep in another room when Mr Pajich was murdered by Lenon.

But Lenon, a submissive in the BDSM scene, claimed it was Lilley who attacked the teenager with a garrotte and a knife as he sat in their home drinking coffee.

Prosecutors successfully argued each woman was equally responsible.

They will be sentenced on February 28.