They'd have to prove that either officer *intended* to deprive the two victims of their civil rights. That would be extremely hard to prove in Ferguson since it seems that was a chance encounter that turned very bad... there might be a chance in NYC since Garner was known in the area for selling loosies and may have been known by the officers involved. Intent still has to be proven, though, so they'd need evidence like statement from the officers that they planned to beat Garner's ass.

Anyway, my point is I think Obama was muted because there wasn't much he could do unilaterally. The Justice Department might have better luck just investigating the departments but that comes with alot of political baggage.