I didn't know this (I knew nothing of his past other than he's worked for outlets all over the spectrum, from Fox News to Reason to HuffPo, and had even been an analyst at Cato, before going to WaPo). Is he any more anti-cop than your usual civil-libertarian reporter?
He made his name on the "rise if the warrior cop". Since then he's beat the drum for every outlet he could find that this is the biggest issue in America today. WTOP had him on air about 2 days after Michael Brown was killed and he was tripping over himself he was so excited trying to blame this on militarized police. He'll occasionally throw out some libertarian pro-pot, pro gay marriage article but they're outnumbered 100 to 1 by his police stuff.
Are you familiar with the meme about the guy from "Ancient Aliens" about how that explains everything? Same level of fanaticism, just swap out "ancient alien" for "militarized cop".