No, it’s not The Onion. It’s an actual letter, in which Bin Laden’s adult sons “demand an inquiry . . . into the fundamental question as to why our father was not arrested and tried but summarily executed without a court of law.” From the letter:
If OBL has been killed in that operation as President of United States has claimed then we are just in questioning as per media reports that why an unarmed man was not arrested and tried in a court of law so that truth is revealed to the people of the world. If he has been summarily executed then, we question the propriety of such assassination where not only international law has been blatantly violated but USA has set a very different example whereby right to have a fair trial, and presumption of innocence until proven guilty by a court of law has been sacrificed on which western society is built and is standing when a trial of OBL was possible for any wrongdoing as that of Iraqi President Sadam Hussein and Serbian President Slobodan Miloševic’. We maintain that arbitrary killing is not a solution to political problems and crime’s adjudication as Justice must be seen to be done.
For what it’s worth, Bin Laden was formally indicted on criminal charges in the Southern District of New York in 1998. If he had wanted an arrest, a criminal trial, and the presumption of innocence, he certainly didn’t lack the opportunity.