Marcy Cruz, the key prosecution witness in the beating of Irish student Natasha McShane, admitted she did not witness the attack and that she had changed her story several times.

McShane, an exchange student from Armagh, was so badly beaten with a baseball bat in the April 2010 incident that she suffered severe brain damage. Several members of her family are in Chicago for the trial.

Cruz, who copped a plea of 22 years, is the chief witness against Heriberto Viramontes, the chief suspect. She now says she waited in the van after smoking marijuana with Viramontes while he said he was going off to rob someone.

"He told me, look at all these white ho's (and) that he wanted to rob one of them," Cruz said.

However, it was also revealed that Viramontes' DNA was not definitively found on the bat that was used in the beating nor was McShane’s, the Chicago Tribune reports.

Neither MacShane nor a friend with her ever saw the attacker’s face and no blood was found in Cruz’s van.

Cruz a former stripper originally told police she got possessions from McShane’s wallet from a man called Jamaica. She admits now she lied.

Cruz, a mother of two, testified that she met Viramontes, who she knew through her boyfriend, on April 23, 2010, at a nightclub called Illusions, had sex in Cruz's minivan and then drove to the Bucktown area.

She said she had drove around with Viramontes. Viramontes then told her he was going off to mug someone and grabbed a baseball bat in the van.

Cruz admitted during withering cross-examination that she gave police three different accounts of what happened that night.

Cruz said Viramontes left the van and returned some time later with two purses..

"He stated that the girls were really pretty and that he did some bogus (stuff)," Cruz testified.

They went to a gas station and used the credit cards and Viramontes gave her a Blackberry, some perfume and makeup from the purses. Video  footage shows the two at the station at 3:48 a.m.

They were later joined by Viramontes' girlfriend and she told her that "he robbed some girls."

Under cross examination by defense attorney Chandra Smith Cruz admitted she lied to police at first about buying the wallets from the man called Jamaica for $80.

"You told that lie to keep yourself out of trouble, right?" Smith asked.

Prosecution lawyers also called Jaclyn Garfinkle, a former Illinois State Police forensic expert, who testified that Viramontes' DNA could be on the bat, but that 1 in 18 Hispanics could not be excluded.

Even Cruz’s father admitted wasn’t sure whether his daughter was being honest.

“There were so many stories there that, I don’t know,” Edwin Cruz said in an interview with the Chicago Sun-Times.