Yang is charged with the October 2007 murder of Rhoni Reuter and her unborn child.
A former boyfriend of Yang also took the witness stand. Salvador Devera testified he and Yang often went to a shooting range for target practice.
He also said she gave him two books on how to make gun silencers.
Yang's former friend, Christi Paschen, is scheduled to take the witness stand on Thursday.
A day earlier, Bears great Shaun Gayle admitted he had a sexual relationship with Yang and that they had sex the night before the murder of his pregnant girlfriend.
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