According to Wikipedia, "Conviction for murder in the absence of a body is possible; although historically, cases of this type have been hard to prove, the prosecution must rely on other evidence, usually circumstantial."
Imagine a fictitious murder trial, where a zealous Attorney General is bringing murder charges against the man who shot Osama bin Laden.
In the absence of Osama bin Laden's body, can the shooter be convicted?
There may be blood, there may be shell casings, but without a body, can the prosecution prove beyond a reasonable doubt that there was in fact murder?
To obtain a conviction in this fictitious trial, the prosecution would have to bring convincing circumstantial evidence, such as, for instance, blood matching bin Laden's DNA, or a tooth matching his dental records, a video of his brains being blown out, or a pile of equally convincing corroborating evidence.
Then there is always the matter to independently verify that the evidence gathered by the prosecution was not falsified.
Notice that I am not proposing any conspiracy theory. I am simply highlighting different types of evidence that a court of law may require for a conviction.