The article Man Outed As Undercover Cop At Occupy Oakland Condemns Police Brutality, Supports The Movement explains:
In a video released last month, Oakland Police Officer Fred Shavies was outed as one of these plainsclothed officers at Occupy Oakland.
The article contains the above mentioned video. The article also includes a video interview with the officer. I find the video interview with the police officer (included below) to be the most compelling part of the article.