Several British newspapers have reported that the identity of James Foley's killer is already known: government sources said that a former British rapper of Egyptian heritage beheaded the US journalist in Syria. According to reports, the hip-hop singer became radicalized and left London for Syria, where several months ago, he tweeted a picture of himself holding the severed head of a man. Officials have not yet confirmed the allegations, but British ambassador to the United States, Peter Westmacott, told CNN that investigators would soon release the killer's name.

Accent provided a clue

In the beheading video that was posted on the Internet, the killer is almost entirely masked. Despite this, investigators found several clues to go on. The focus has been on the man in the video speaking Islamic propaganda with an unmistakable British accent. John O'Regan, a linguist at the University of London's Institute of Education, said the man's origin can be even more clearly pinpointed, as he speaks what is known as multicultural London English. The man was making an effort to speak formally, O'Regan told the Associate Press news agency, as evidenced by his emphasis on the exact pronunciation of the letters p and q.

The voice reveals even more, according to German broadcaster ARD's terrorism expert, Paul Elmar Jöris. "When forming sounds, every person's voice has certain characteristics, due to the jaw," he said. "These characteristics cannot be changed, and we have equipment that can produce a graphic image of them." Based on the pattern created, investigators can compare voice samples.

Acoustic comparison

Intelligence services such as the FBI and the British Secret Service, which are investigating the Foley murder, can draw on other online videos or samples taken from phone conversations to hone in on possible suspects. The German Federal Criminal Police Office (BKA) and Interpol as well as Germany's Criminal Investigation Department can also call on the services of speech recognition experts.

In addition, investigators have been questioning witnesses from the suspects' milieu, said Jöris. "You do a sort of acoustic comparison, so that forensically, you can be certain that you've got the right guy," he said. According to the British media, the radical Islamist's former hostages recognized the voice as belonging to one of their guards; they also presumed British heritage.

Detailed image analysis

It's not just the killer's voice that has provided investigators with clues as to his identity. His eyes look into the camera through a small slit in the fabric covering his face. "You can get an exact measurement on the space between the eyes," said Jöris. Once a certain number of unchangeable characteristics have been found, it's possible to identify a person, he added. The investigators use everything at their disposal: height, stature, even the pattern of veins visible on the back of the man's hands. However, they need to have photo evidence that can serve as a basis for comparison.

In the age of social networking, though, that seems to hardly be an issue. The majority of Islamic State's mostly young members have Facebook or Twitter accounts. Many of them continue to post items directly from the war zone to boast about their crimes. Peter Neumann of King's College in London believes they simply can't help themselves. "They are extremely rooted in online culture," said the expert on radicalization, adding that many of the fighters can't break the habit of posting photos of themselves.

Traces on the Internet

Those who don't use their real names on social networking sites still reveal much about their background and their social environment. Even Islamic extremists who decapitate people will still post about their favorite soccer teams online, said Neumann. It frequently doesn't take long to gather a lot of information about a suspect.

The Internet plays another important role when it comes to tracking down suspects: IT experts can attempt to trace the origin of an uploaded video back to a certain country, a certain region, even a certain computer. Digital data can reveal plenty of information, as do the images themselves.

A seemingly neutral desert landscape in the background, for example, can be compared with geological data. Noises from the environment can also help investigators pinpoint a region. For tasks such as this, Germany has for six years now maintained the GIZ (Common Internet Center) under the leadership of the Federal Office for the Protection of the Constitution in Berlin.

Many contributors

"When they have such sequences, they're not just analyzed by one researcher," said terrorism expert Jöris. Many people play a part in ensuring that the lead investigators are successful.

Technology undoubtedly plays an important role, as does police questioning of witnesses. In Britain, many Muslim religious leaders have condemned the murder of James Foley and called on anyone who may know the perpetrators to get in touch with the authorities. In the end, it could be old-style police work that leads to the capture of the US journalist's killers.