Rochester N.Y.- Sentencing has been delayed for three weeks for Dawn Nguyen .

She pleaded guilty to federal charges stemming from the illegal purchase of the guns used in the West Webster ambush on Christmas Eve 2012.

Nguyen's lawyer, Matt Parrinello asked for a postponement. He is planning to challenge the government's request for a punishment that is tougher than recommended by sentencing guidelines.

Nguyen is already serving prison time on related state charges. She bought the guns for William Spengler, who used them to kill his sister and two firefighters.

Sentencing is now set for September 17th.