The State and the federal governments are referred to as 'separate soverigns.'
Each sovereign has the right to prosecute any crimes that are done against its own laws.
The States of Maryland, Virginia, Washington, and now, Louisiana, are all empowered, as sovereign governments the right to prosecute crimes occurring within their borders.
The Federal government may also prosecute any crimes as defined by its own laws.
This is the way it has been since the founding of the Republic, and should not offend anyone's sensibilities, at all.
There are different laws and procedures that attach to each sovereign's enforcement of its laws.
For examply, Malvo, being 17 years of age, cannot receive the death penalty in Virginia, while Muhammad can.
In Louisiana, Malvo can be tried and executed for the murder of the store clerk, if it occurred during the commission of an armed robbery (which it did), and if the state can prove that he, and not Muhammad, was the shooter.
The laws of evidence may also differ from state to state, with the federal government having its own Rules of Criminal Procedure.
So, all in all, it makes good sense.
Eric The(Legal)Hun[>]:)]