(Portland, OR)  --  A man who's accused in the murder of Ashley Benson says he's not guilty.  Tae Bum Yoon entered the plea yesterday in a Multnomah County courtroom to charges of murder and first-degree manslaughter.  Benson was found dead on December 26th at a Northeast Portland hotel.  Investigators say Benson met Yoon through an ad on Backpage.com.