Bulgarian police, the FBI and Interpol are struggling to identify a suicide bomber who killed six people, including five Israelis, in an attack at the Black Sea airport of Burgas this week.
Investigators have released CCTV footage of the person they believe carried out Wednesday's attack on a bus carrying Israeli holidaymakers, which also claimed the life of the Bulgarian driver.
After two days of investigations, Tsvetan Tsvetanov, Bulgaria's interior minister, was only able to confirm on Friday that the bomber was "not a Bulgarian citizen" and had been in the country "not less than four days".
Fingerprints and DNA samples from the suspected bomber's body were being used in the effort to learn his identity, he said.
The minister also made public on Friday evening some scanty details on the explosive that was used in the attack, which was the first of its kind in Bulgaria.
"We are speaking about trotile, about 3kgs. Analyses are continuing," he told state BNT television. Trotile is made from Trinitrotoluene or TNT - a common material in military bombs that is also frequently used in attacks by fighters.
Israel and Bulgaria, meanwhile, held funerals for the victims - Israelis Kochava Shriki, 44, who was pregnant, Yitzhik Kolengi, Amir Menashe, Elior Priess and Maor Harush, all in their 20s, and the Bulgarian driver of the bus Mustafa Kyosov, 36.
More than 30 people were also injured in the blast, three of them seriously, all of whom have since been repatriated, as have around 60 others who escaped injury. Some opted to continue their holiday at the Black Sea resorts popular with Israelis.
Identifying the bomber
Airport video footage of the presumed suicide bomber, released by Bulgarian authorities, showed an apparently white male with long hair, possibly a wig, dressed in typical holiday gear - shorts, a baseball cap, sneakers - and carrying a backpack and a laptop bag.
Tsvetanov said the man, who was shown wandering around the airport, looked to be around 36 years of age. Investigators have also recovered his drivers licence from the US state of Michigan that is thought to be fake.
The name on the licence, an image of which was shown on Bulgarian television, is Jacque Felipe Martin of Baton Rouge, Louisiana, born in 1987. Michigan is known to only issue licences to state residents.
Bulgarian prosecutor Kalina Chapkanova told private BTV television on Friday that the suspect used the fake licence when he tried to rent a car in the nearby town of Pomorie a day before the attack.
The car rental owner turned him down as the document seemed suspicious.
Interpol has sent an "incident response team" to Bulgaria including two terrorism experts from Switzerland and France and a US explosives specialist. European police agency Europol was also assisting.
The explosion ripped through the bus as around 50 Israeli tourists arriving from Tel Aviv were loading their bags before travelling to nearby holiday resort of Sunny Beach.
The bomber struck on the 18th anniversary of an attack on a Jewish community centre in Argentina that killed 85 people.