How death of al-Zawahiri means that ALL 9/11 plotters have been killed or imprisoned 

The execution of Ayman al-Zawahiri marks 21 years of US intelligence forces and military tirelessly hunting down those responsible for America’s worst terror attack.

On September 11 2001, 2,973 people died and thousands were injured as two hijacked planes flew into the twin towers of the World Trade Center in New York City.

Two other planes were crashed into the west wall of the Pentagon in northern Virginia, and a farm field in Shanksville, Pennsylvania.

Osama bin Laden plotted with al-Zawahiri, his number two, to carry out the violent attacks in the US along with six other men in Afghanistan.

The two terrorists reportedly met sometime in late 1980s, when al-Zawahiri kept the Saudi millionaire safe in the caves of Afghanistan from Soviet bombardments that were common in the region.