Why was Anwar al-Awlaki executed by drone, without due process?

[bhikkhu]

62. "The use of poisons of chemical and biological weapons against population centers is allowed"

"The use of poisons of chemical and biological weapons against population centers is allowed and strongly recommended due to the effect on the enemy," al-Awlaki continued. He then quoted several religious scholars to justify such attacks, concluding: "These statements of the scholars show that it is allowed to use poison or other methods of mass killing against the disbelievers who are at war with us."

...that's just one statement. Guys like him are the reason there has been a war, and the reason so many civilians have been killed. He spoke with and probably influenced three of the 9/11 hijackers, he counselled the Fort Hood shooter, and the "underwear bomber". He fled to Yemen, where he advocated the most merciless and inhumane type of general war. He hid out with a private army. Yemen tried to arrest him, but they were apparently out-gunned.

Its very hard to compare him with anyone else, he was pretty uniquely outspoken and influential, and effective. You have to work very hard to get on that list.

If you were president, and actually responsible to protect against people like that, what would you do?

on edit - the link for that quote: http://security.blogs.cnn.com/2012/05/02/from-the-grave-al-awlaki-calls-for-bio-chem-attacks-on-the-u-s/