Let all of them go, or file charges against all of them. The fact that officers involved, and district attorneys are "picking and choosing" who to file charges against, is a problem to me. And could easily lead to racial bias issues, socioeconomic discrimination, and gender bias...meaning that men may get a pass, but women don't...Ross Harris was texting a girlfriend, therefore, it is "logical" to assume that he did intend to kill his child. (Note, I am definitely not championing RH!).
Charge them all. And personally, I think people who leave dogs in their car should be charged as well.