ISIS's brutal beheading video: Search for clues

It was a killing choreographed for maximum brutality: The simultaneous beheading of 22 Syrian captives held by ISIS.
In November, ISIS released a propaganda video titled "Though the Unbelievers Despise It." It featured the apparent murder of an American hostage, Peter Kassig (known as Abdul Rahman Kassig after his conversion to Islam), and the mass killing of what appear to be nearly two dozen Syrian soldiers.
The US-based terrorism research organization TRAC (Terrorism Research & Analysis Consortium) and UK-based counter-extremism think tank Quilliam have analyzed the footage frame-by-frame to understand the video's production techniques, the identity of the hostages and their killers, and the visual significance of such calculated brutality.
Here are some of their findings:

• The video would have cost at least $200,000 to produce, according to TRAC. Similar to a feature film, the video features multiple takes using HD cameras to create images of a professional quality.
• Nearly all the killers appear unmasked and are clearly identifiable. There are 22 ISIS fighters of varying ethnicities and nationalities, all wearing the same camouflage uniforms. They are led by the militant known to the British press as "Jihadi John," the masked fighter with a British accent responsible for the killing of western hostages.
• Only one of the killers has been identified: Maxime Hauchard, a Muslim convert from France. Several other countries are now investigating whether any of their citizens are in the video.
• Lighting and shadows reveal the video was shot over a 4 to 6 hour period. The video was shot in multiple takes, and contains several inconsistencies. The order of the killers and prisoners in the line-up is switched in several places. In certain frames, fighters are seen chatting with one another, apparently passing time between takes.
• Two of the ISIS fighters wear clip-on microphones, but their audio is not recorded. It's possible their recorded messages were either cut out or have been saved for a future release.
• Three of the killers are have been edited out of the video, seen only in transitional sequences. This includes a fighter in a balaclava, the only masked militant other than "Jihadi John." TRAC believes the second masked militant may be acting as a body double for "Jihadi John," someone who acts as a decoy in case of an airstrike.