> as he was murdered in a foreign country, no court in the US has jurisdiction for the president to be prosecuted

You're underestimating the creativity of prosecutors. :)

For example, they could have charged him with conspiracy to commit murder in any location where Obama met with others to discuss killing al-Awlaki.

Or a future president, like Trump, could have pressured a federal prosecutors to bring charges in Federal Court, since they can bring charges for crimes committed against Americans globally.