1. Accent
The focus has been on a man in the video who has a British accent. Peter Westmacott, British ambassador to the United States, said Sunday that British agents have been using "very sophisticated technologies, voice identification and so on" to identify the suspect. "We are very close to identifying who this guy is," he said.
Martin Barry, an audio expert, told CNN it sounded like the way someone in a certain area of London would talk.
"The speaker is using a variety of English known as multicultural London English and that's a kind of melting pot accent that's emerged in recent years, particularly in deprived, multi-ethnic areas of inner London," Barry said.
There is only one voice heard on the audio track.
2. Stature
But Ross Patel, a forensics expert who spoke to CNN, said there is another man, and he might be the actual killer.
The second militant appears on the video after an obvious edit.
"There's definitely a change of actor," Patel said. "There are noticeable, there are subtle but there are also noticeable changes in their build, their physical appearance."
3. Knives
The man who speaks holds a knife in one of his hands. It looks to be a different knife than the one that was left next to Foley's body.
The dimensions and style of the knives are slightly different, Patel said.
4. Holster
When trying to determine whether the British-accented man is also the killer, it helps to examine where his pistol is holstered. It is underneath his left armpit -- that is for use by his right hand. But the executioner appears on the video to be left-handed. It's unclear why this happened.
5. Location
Blogger Eliot Higgins looked at the background of the video. Behind the men is a road going over the hilly terrain. On the right side of the frame is a dip in the hills, one Higgins matched to a break he found in an image on Google Earth. There was another camera angle used in the video and in the distance there is a field and some buildings. He believes the clues show the video was recorded south of the town of Raqqa in north central Syria