It appears to me that there is some confusion about what the issue was with the Martin/Zimmerman case.
The reason so many people got upset about Zimmerman was not just because of what he did but the sense, that from the beginning, that he could act with impunity. This is the heart of the outcry over what happened, not that "OMG a white man killed a black kid!" Had he been arrested right away, even if in the end, charges were dropped I doubt this would have had the legs that it did. The anguished reaction in the black community was not that so much that we are under constant threat from "white violence" but from the sense that what was historically true might still be true today, that a white person can commit violence against a black person and expect to walk free. There is fear that this knowledge might embolden some people to do things they might not do otherwise, believing that there will be no consequences.
And so bringing up cases like this horrific shooting of Chris Lane misses the point. Unless it appears that these young thugs are going to walk free, there is no equivalence between this and Trayvon Martin.
BTW, as has been noted one of the three teens involved in Lane's shooting was white. He appears to be getting somewhat lighter treatment. Bail has been set for him but denied for the others etc. I guess he was just the driver of the car rather than the actual shooter so perhaps that's why (though there was only one shooter, the other two were egging him on). I feel the same about all three of them though as I did about Zimmerman. I hope they are found guilty and pay for their crimes. The main difference is unlike with Zimmerman, I'm pretty sure that's exactly what will happen.