the charges against sleepy dan, logan's former roommate who he helped the police bust, have since been lethal dose remains at large. francesca would use her dead son's phone one last time to text that anonymous dealer a message. you texted that boy, didn't you, that young man? >> yes. >> reporter: what did you say? >> you killed my son. and i hope -- i hope you rot in hell. >> reporter: just this week, "20/20" has learned that phone number belonged to a paid teacher's assistant at umass according to a university directory. he is no longer at the school, and the open investigation is now in the hands of the local district attorney. the dealer, what has happened to him? >> nothing happened to him, as far as i know, nothing. >> reporter: he hasn't been arrested? >> no. >> reporter: why wouldn't they go after a dealer who gave another student a deadly dose of heroin? >> maybe they made him a confidential informant. >>> so, what do you think? did the police make a crucial wrong decision by not arresting logan? >> and c that's the way i look at life. looking for something better. especially