An eyewitness and his pictures document a Syrian scene meant to send a message
Bodies are strung up on crosses in the city of Raqqa
An al Qaeda splinter group -- ISIS -- says it's a lesson for any who dare challenge it
An effort is underway by local activists to try to push ISIS out of Raqqa
It is a scene seared forever into the memory of an eyewitness:
Masked men drag the bloodied body of a man across a public square, and tie it to a make-shift cross on a metal pole.
Green string holds the body’s arms outstretched across a wood plank as blood oozes from the gunshot wound to his head.
Militiamen wrap the body’s black “WhatsApp” shirt with a sign in red letters that reads in Arabic: “This man fought Muslims and detonated an IED here.”