ABC7 News has obtained several documents used in Yang's trial including an invoice for the first two volumes of a book she ordered called "How to Make Disposable Silencers".
ABC7 also obtained surveillance video showing Yang at a Home Depot store on the same day she received those books buying the items needed to make a silencer.
Last month, a jury found Yang guilty of murdering Reuter and her unborn child.
Prosecutors said yang was jealous over Reuter's relationship with former Chicago Bear Shaun Gayle.
