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NYPD faces backlash as it prepares to encrypt radio communications | New York | The Guardian
(www.theguardian.com)
This is a most excellent place for technology news and articles.
The American legal system has made a conscious decision to require public trials (so accused are public) with the right to face your accuser (so victims are public). This does remove privacy, but the idea is that the trade off is worth it to avoid people being "convinced" in secret trials.
You may disagree with this trade off, but it's baked in and changing it would be a big difference. Some exceptions exist, I think, but IANAL.
Obviously nobody should disappear into secret jails, but victims and witnesses are not on trial, and should have their privacy protected.
Having random people listening to police comms is no substitute for a competent regulator.