In most cases murder is a state crime. However, Washington, DC is not covered within any state's jurisdiction. My question is whether the President can pardon someone for committing murder if the crime took place within the geographical boundaries of DC.
The Department of Justice's Office of the Pardon attorney says yes:
Under the Constitution, only federal criminal convictions, such as those adjudicated in the United States District Courts, may be pardoned by the President. In addition, the President's pardon power extends to convictions adjudicated in the Superior Court of the District of Columbia and military court-martial proceedings.
Like other felonies committed in the District, murder charges are adjudicated by federal prosecutors in the Superior Court, so they would fall within the scope of the presidential pardon power, as interpreted by the DOJ.
Not only is the President allowed to pardon crimes under the DC Code, only the President is allowed to pardon (most) crimes under the DC Code. While the DC Council has the power to pass criminal laws for the District, it acts under delegated federal authority and the offenses it creates are offenses against the United States. The prosecuting authority for all felonies and some misdemeanors is the US Attorney’s Office for the District of Columbia, and the cases are brought in the name of the United States. As offenses against the United States, the President can pardon them. It happens to be rare, but has happened (Alfred J. Mack was pardoned of a DC Code offense).
Some territories have laws giving their chief executive the power to pardon territorial crimes. DC does not. It gives limited pardon powers to the mayor, but those apply only to minor crimes enacted by long-defunct city governments and which have virtually all been repealed since at least 1901, as well as to certain regulatory offenses. Murder is on the complete opposite end of the spectrum, so the DC mayor’s pardon authority doesn’t extend to murder charges (whether prosecuted under the DC Code or the US Code). In territories like Puerto Rico that give their governor pardon power, the norm is that the President doesn’t try to issue his own pardons for territorial crimes (he might be able to, but it hasn’t really been tested). In DC, there’s no such norm because prosecution of serious crimes is an entirely federal matter anyway.