Why would we have heard about any of the failures? Part of the 'blue wall' is intended to hide policing failures from the general populace. Particularly when
* in the case of targeting a well off person who they decide to further investigate, they can simply use it as reason to look harder at someone, use parallel construction to build the case that the defense sees, and simply drop any cases where the defense happens to get too close. This is what they do with stingrays.
* in the case of targeting a well off person who they decide not to investigate, they can simply tell themselves that the person is a paragon of society and it must be one of the failures of the technology. Like when a boy escaped Jeffrey Dahmer's house heavily drugged, running down the street, bleeding out of his anus, begging anyone who would listen to not let Jeffrey take him back, the police got involved and gave him back since Jeffrey was such a paragon of the town. That cop later became head of the police union.
* in the case of targeting a well off person who they decide to further investigate, they can simply use it as reason to look harder at someone, use parallel construction to build the case that the defense sees, and simply drop any cases where the defense happens to get too close. This is what they do with stingrays.
* in the case of targeting a well off person who they decide not to investigate, they can simply tell themselves that the person is a paragon of society and it must be one of the failures of the technology. Like when a boy escaped Jeffrey Dahmer's house heavily drugged, running down the street, bleeding out of his anus, begging anyone who would listen to not let Jeffrey take him back, the police got involved and gave him back since Jeffrey was such a paragon of the town. That cop later became head of the police union.