A dispute over DNA on a baseball bat allegedly used in the brutal attack of Irish student Natasha McShane in Chicago, is delaying the criminal trial of those accused of her attempted murder.

McShane, now 26, was viciously assaulted three years ago, as she and her friend Stacy Jurich walked home in the early hours of the morning. The two young women were attacked from behind with a baseball bat after a night out in the Wicker Park-Bucktown area of the city.

The Irish student from Co. Armagh was in Chicago on an exchange program at the University of Illinois when the assault took place. Speaking to the media last year, her father described how the young woman was struggling with basic functions, like speaking and dressing herself.

Now a battle over DNA evidence taken from the baseball allegedly used in the attack is causing a delay in the trial, the Irish Independent reports.

Heriberto Viramontes, 34, is accused of perpetrating the assault and faces a first degree attempted murder charge.

The co-accused and girlfriend Marcy Cruz, 28, also faces 25 charges ranging from attempted murder to credit card theft.

A picture of Natasha McShane taken before the vicious assault in April 2010Handout