LACROSSE, Wis.— Through DNA tracking, police have made an arrest for sexual assault 15 years ago.  Arrested was Mitchell Lisowksi, now 38, of Blair.  At the time the victim reported that she met her assailant on a bus, that he said he was from Eau Claire and that had gotten separated from friends and needed help finding them. The woman said she allowed him into her apartment, which she said led to unwanted sexual advances and penetration. Police collected DNA at the time but no matches showed in data bases until recently.