Quis custodiet ipsos custodes?

http://www.bbc.co.uk/news/uk-england-wiltshire-11787126

How this officer, Sgt Mark Andrews, has escape the prison sentence he so thoroughly deserves completely eludes me.  For those unfamiliar with the back story; Ms Somerville was arrested after she was found asleep in her car, she was detained after failing to provide a sample for a breath test.  So firstly she had not injured anyone by drink driving (no victim), she was exercising self ownership by refusing to allow the officer to take breath samples from her (again no victim) and was not even prosecuted for any crime following this event (so clearly not a criminal).

How can anyone justify this treatment of an innocent person, especially considering the above?  The woman had not committed a crime and never once assaulted the officer, therefore we should not care for Mr Andrews' excuses. Whether Ms Somerville was "unpredictable", "abusive" (despite no evidence to substantiate these claims) or needed to be forced into her cell, the injuries she received were without warrant.

It seems absurd to me that someone can be arrested and beaten for sleeping in their own car, yet a police officer can be witnessed assaulting an individual and receive no reprimand.  Should we not judge all members of society by their actions rather than their motives?  Why should the law enforcers abide by their own privileged set of rules?

Quis custodiet ipsos custodes?