My understanding is large stores of Iraqi Army (read:US) have been captured. Tanks, arty, small arms,etc. $400 million bank robbery. Can beheadings on a MASSIVE scale be far off?
Why did they fold so quickly you ask?
The answer is all the Sunni in the military hold more of an alliance to their fellow Sunni radicals than they do to the country/flag of Iraq. The only reason they joined the Iraqi military in the last 10 years was to survive/eat. Live to fight another day. The Sunnis will end up controlling the northwestern part of Iraq. The Kurds will control the northeastern part. The Shiite will align with Iran and control the southern part. It is inevitable unless another dictator emerges that wants it all and will to kill a million people to do it.
Fairly easy to 'splain...the ISIS group are more than willing to die for their cause; the Iraqi army are not willing to die for anything. Hence, the running shoe is the most important item of the Iraqi army.