There is one huge red flag in this and that is he involvement of the FBI.

If it was just the kidnapping and murder of a child and all of the elements of the crime occurred within Texas, the FBI would have no jurisdiction.

What WOULD give them jurisdiction is if they had evidence of a conspiracy to deprive D Brown of his civil rights, or offical misconduct under color of law involving a civil rights violation.

Another possibility as has been pointed out before is if child pornography was involved, or some sort of conspiracy that extended across state lines.

The FBI is going to clear D Brown.

There is too much bullshit involved, including the police first claiming Brown as GPS tacked and then denying it hen we can clearly see the ankle monitor in the video. That to me indicates a conspiracy ON THEIR PART to deprive Brown of his civil rights.
With the reputation the DPD has for institutionalized racism it is a sure bet the DOJ and FBI was already investigating them continuously before this even happened.

There is some other reason besides the evidence directly involved in this case that the charges of murder have not been brought against anyone yet. The FBI has no doubt determined that it was impossible for Brown to have done what he is accused of.