Records show a Los Angeles police officer shocked a handcuffed woman with a stun gun while joking with fellow officers, in an incident caught on video.
An investigation by the Los Angeles Times finds Officer Jorge Santander then appeared to lie about the December 2010 encounter repeatedly in written reports.
The newspaper finds three other officers who witnessed the incident all corroborated Santander's version of events when first questioned. They also failed to tell supervisors that one officer had recorded it on video.
Prosecutors declined to charge Santander.
Police officials say Chief Charlie Beck is seeking to have Santander and the three others fired.
The Times says it is the fourth case made public in the last few months in which LAPD officers are accused of using force on suspects who were restrained.