I hate that this happens to anybody, and I send sympathy to the families. Nevertheless, I do not see enough in this article to explain what really happened.
It is possible that the police have swept aside cases involving green-card holders, but there are so many unsolved murder cases of Americans that I would have to see better statistics from a reliable source to believe that the problem is specific. It is also alleged that American police do not give as much effort to solving black American crimes as white American crimes, but I also just saw a story about a white couple who reported their baby Sabrina missing, and the white prosecutor went so far as to falsify evidence to try to convict the couple of killing their own child.
I have done what I could to make sure that the right thing gets done when I see injustice around me, and I have been hurt repeatedly for it. The same has happened with others that I know or know of.
It is only when enough of us are willing to do the right thing despite the consequences that things will get better. That can be difficult, especially when the consequences are not just to the individual, but when children or a family counts on the individual to provide for them.
Once the critical mass is met and enough people are willing to stand up for the right thing, evil will no longer have such a stranglehold. Until then, we must encourage everyone we can, and set the example of doing the right thing no matter what. If we all stand for justice, it will only hurt for a little while and the rewards will be great.