Zimmerman has no ability to have a government prosecutor file charges on his behalf.
He will ultimately have the ability to file personal lawsuits, not criminal cases, against a whole host of people.
In personal lawsuits, you cannot ask for a death penalty.
Only the government has the ability to seek and execute a death penalty.
Except that it seems fairly obvious to me that the government agents have violated the law; Sec 241 & 242 of US Code Title 18.