I'm just listening to Lawyer Lee's update for yesterday, and at around the 50 min mark in her video, she explains why the prosecution moved to admit this. They argued the defense had opened the door to it, during their cross-examination of Harshman, when Rozzi asked him;
1. have you been listening to phone calls of his in the last 3 weeks, and would this be a really stressful time coming into trial?
2. have there been times where he's proclaimed his innocence?
3. have you ever seen him pose a threat to anyone at Westville?