There have been a lot of questions and concerns that the DOJ cannot do much. Not so. According to the Department of Justice website, they could possibly indict for use of excessive force, if they find sufficient evidence to believe a crime was committed.
Federal Criminal Enforcement
It is a crime for one or more persons acting under color of law willfully to deprive or conspire to deprive another person of any right protected by the Constitution or laws of the United States. (18 U.S.C. §§ 241, 242). "Color of law" simply means that the person doing the act is using power given to him or her by a governmental agency (local, State, or Federal). A law enforcement officer acts "under color of law" even if he or she is exceeding his or her rightful power. The types of law enforcement misconduct covered by these laws include excessive force, sexual assault, intentional false arrests, or the intentional fabrication of evidence resulting in a loss of liberty to another. Enforcement of these provisions does not require that any racial, religious, or other discriminatory motive existed. What remedies are available under these laws? Violations of these laws are punishable by fine and/or imprisonment.
Shooting an unarmed man in the circumstances as witnesses have described would appear to constitute "excessive force" under the meaning of the statute.
Congressman Clay and others trust DOJ, but do not trust McCulloch. From last Friday:
As the investigation has unfolded, McCulloch has been criticized by some local politicians. U.S. Rep. William Lacy Clay, D-St. Louis, who also appeared on CNN's "State of the Union," said in an appearance in Ferguson Friday night that "we don't have any confidence in the St. Louis County prosecuting attorney's office."
“Bob McCulloch tried to taint the jury pool by the stunt he pulled today," Clay said Friday night, referring to the convenience store videotape. "I have no faith in him, but I do trust the FBI and the Justice Department.”
Post Dispatch
DOJ should not wait for McCulloch to slow walk the grand jury through mid-October. If the evidence warrants an indictment, they should go first and indict.
Update I: The punishment in the statutes is bolded below:
18 U.S. Code § 241 - Conspiracy against rights
If two or more persons conspire to injure, oppress, threaten, or intimidate any person in any State, Territory, Commonwealth, Possession, or District in the free exercise or enjoyment of any right or privilege secured to him by the Constitution or laws of the United States, or because of his having so exercised the same; or
If two or more persons go in disguise on the highway, or on the premises of another, with intent to prevent or hinder his free exercise or enjoyment of any right or privilege so secured—
They shall be fined under this title or imprisoned not more than ten years, or both; and if death results from the acts committed in violation of this section or if such acts include kidnapping or an attempt to kidnap, aggravated sexual abuse or an attempt to commit aggravated sexual abuse, or an attempt to kill, they shall be fined under this title or imprisoned for any term of years or for life, or both, or may be sentenced to death.
18 U.S. Code § 242 - Deprivation of rights under color of law
Whoever, under color of any law, statute, ordinance, regulation, or custom, willfully subjects any person in any State, Territory, Commonwealth, Possession, or District to the deprivation of any rights, privileges, or immunities secured or protected by the Constitution or laws of the United States, or to different punishments, pains, or penalties, on account of such person being an alien, or by reason of his color, or race, than are prescribed for the punishment of citizens, shall be fined under this title or imprisoned not more than one year, or both; and if bodily injury results from the acts committed in violation of this section or if such acts include the use, attempted use, or threatened use of a dangerous weapon, explosives, or fire, shall be fined under this title or imprisoned not more than ten years, or both; and if death results from the acts committed in violation of this section or if such acts include kidnapping or an attempt to kidnap, aggravated sexual abuse, or an attempt to commit aggravated sexual abuse, or an attempt to kill, shall be fined under this title, or imprisoned for any term of years or for life, or both, or may be sentenced to death.