Defense attorneys preparing for the first-degree murder trial of a Raleigh woman accused of killing her husband's ex-girlfriend now want access to a knife that they say police found Friday in their client's SUV.

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In a motion filed Monday, attorney Johnny Gaskins says the weapon had been hidden in the center console of Amanda Hayes' 2009 Dodge Durango and that it could bolster their defense that it was Hayes' husband, Grant Hayes, who killed Laura Ackerson on July 13, 2011.

The 27-year-old's dismembered remains were found 11 days later in a creek in Richmond, Texas, near the home of Amanda Hayes' sister.

The Hayeses were arrested July 25, 2011, and Grant Hayes was found guilty of Ackerson's murder in September.

Any involvement Amanda Hayes might have had, her defense has said in court documents, was while she was under duress and fearful for her life.

"The 'knife' that was found in the Dodge Durango by the Raleigh Police Department appears to be yet further evidence that the defendant's husband, (Grant Hayes), was prepared to kill the defendant and their children while they (were) in the Dodge Durango …" Gaskins wrote in Monday's motion.

He does not indicate what kind of knife was found, saying the state has not yet provided the defense with any other information.

Gaskins goes on to say that Grant Hayes had threatened to kill Amanda Hayes and their children – two young sons he had with Ackerson and a 1-month-old daughter he had with Amanda Hayes – with a machete.

Grant Hayes also threatened his wife in a letter he wrote to her while they were both in jail, Gaskins says in the motion.

Superior Court Judge Paul Ridgeway granted the motion for testing, as well as testing of a biohazard suit and pair of rubber gloves also found recently in the SUV, which has been in police custody since the Hayeses were arrested.

Prosecutors say that the suit and gloves belonged to Raleigh police investigators who wore the items to keep from contaminating the vehicle and were left as part of normal procedure.

Amanda Hayes, who is also accused of accessory after the fact to murder, goes to trial the week of Jan. 20, and if convicted of first-degree murder, faces life in prison without the possibility of parole.

The state hasn't said how she was involved in Ackerson's death but has indicated that Amanda Hayes and her husband were equally culpable of the crime.

During his trial, Grant Hayes' defense attorneys argued Amanda Hayes killed Ackerson during an argument and that he was guilty only of trying to protect her by covering up the crime.

Prosecutors say Grant Hayes killed Ackerson, in part, because of a bitter custody battle over their sons.