Why file Nol pros?

My boyfriend is in the middle of court proceedings. He had a hearing where the judge found that the police officer violated his 4th admendment however the judge gave the D.A. 30 days to file a brief. Before the 30 days were past the Public defender told my boyfriend that his assistant(?) was going to file a nol pros. Why would they do this? Is this good news? I appreciate any information on this topic. Thank you.