The shocking video of James Foley being beheaded in Syria has set off multiple investigations into the mystery of who killed the American journalist.

A day after the British ambassador to the United States said that experts in his country are close to identifying the killer, two U.S. law enforcement officials told CNN that counterterrorism experts are still unable to ID Foley's executioner.

U.S. analysts said it's not knowable from the video released by ISIS who carried out Foley's killing, because the entire slaying is not shown. A man moves a knife across Foley's neck, then the picture fades to black.

Now one forensics expert has raised the issue that there appear to be two militants in the video.

It's one of several puzzles, but there are a number of clues as to who committed this horrible act and where.

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.

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."

The video contains other data like the measurements of a face, even though it is hidden. That could help investigators sift through databases of passport photos.

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.

(CNN)