The quick backstory: LAPD patrol cars are fitted with devices to videotape traffic stops and encounters, and officers wear transponders on their belts that capture audio and send it back to the vehicle recorder via an antenna on the car. In summer 2013 an internal LAPD audit found that antennas on patrol cars had been removed. Doing so doesn't disable the recorder, but it lessens the range over which it works.
After the investigation, Police Chief Charlie Beck told a then-recently-elected Police Commission member who's now the commission president, Steve Soboroff, about the problem and said that it had been resolved, with measures put in place to deter future incidents. But it went no further than that until this February, when the Commission noticed poor quality recordings being used in a shooting investigation; that's when the oversight board was officially informed of the tampering.
Chief Beck, an assistant chief and two deputy chiefs publicly apologized to the Commission this week, saying that the department "fell short" but that "The department did not try to hide this issue." The policemen also defended their decision not to conduct an investigation, saying it would be futile since numerous officers will use a single car throughout the day and there'd be no way to figure out who removed the antennas.
The chiefs said they have developed new protocols to ensure there's no more tampering, including officers documenting the presence of antennas at the beginning and end of each shift and spot checks by supervisors, but it isn't clear that the situation is solved: one antenna has been found missing, and "dozens" of the transmitters worn by officers "were found missing or damaged" in one single division.