One year since U.S. commandos flew into this Pakistani army town and killed Usama bin Laden, Islamabad has failed to answer tough questions over whether its security forces were protecting the world's most wanted terrorist.

Partly as a result, fallout from the raid still poisons relations between Washington and Pakistan, where anti-American sentiment, support for Islamist extremism and anger at the violation of sovereignty in the operation can be summed up by a Twitter hashtag doing the rounds: 02MayBlackDay.

The Pakistani government initially welcomed the raid that killed bin Laden in his three-story compound, but within hours the mood changed as it became clear that Pakistan's army was cut out of the operation. Any discussions over how bin Laden managed to stay undetected in Pakistan were drowned out in anger at what the army portrayed as a treacherous act by a supposed ally.

That bin Laden was living with his family near Pakistan's version of West Point -- not in a cave in the mountains as many had guessed -- raised eyebrows in the West.