One of the 12 suspects held in connection with the Paris attacks might have been a "fourth" gunman.
he suspect's DNA was found on a semi-automatic pistol used by Amedy Coulibaly in his attack on the kosher supermarket on January 9. It was used to shoot and injure a jogger two days earlier.
The eight men and four women were arrested on Friday and are being questioned over whether they helped Said and Cherif Kouachi, who attacked Charlie Hebdo magazine offices on January 7 killing 12 people, and Coulibaly, who killed a policewoman on January 8 and four hostages in a Jewish supermarket the next day.
Investigators are trying to establish who shot the jogger, a 32-year-old electrician who is now in a coma. Before losing consciousness, he is believed to have described his attacker as being "of European appearance", which would rule out Coulibaly. The motive might have been to "test" the gun.
This is part of an inquiry into how Coulibaly and the Kouachis obtained the guns and ammunition, worth about €25,000. As all three had only menial jobs they are unlikely to have had access to such ready funds.
Sarajevo sources say the bullets came from Bosnia. They were 7.62x39mm, a calibre compatible with the Kalashnikovs used by the Kouachis and a sub-machine gun seen in Coulibaly's "martyrdom" video.
Zivko Marjanac, Bosnia's deputy defence minister, confirmed that the ammunition used was manufactured in 1986 by Igman Company, a state-owned factory in Konjic. The company is one of the five largest ammunition manufacturers in the world, supplying more than 30 countries.
Bullets have been stolen from Igman stockpiles in the past but Mr Marjanac emphasised that the bullets were produced almost 30 years ago and it was impossible to establish how they reached France.
"The ammunition was definitely produced in Bosnia. We had a war here; every other house has 20 bullets hidden inside somewhere," he said.
Bosnia was probably the source of the weapons too. Experts believe that about 750,000 illegal firearms are still circulating there; a legacy of the country's civil war between 1992 and 1995.
The Kouachis used an M80 Zolja rocket launcher, commonly used in the Balkans conflict. Coulibaly had a Czech-made VZ58 sub-machine gun, seen in his "martyrdom" video.
"Its shape is symbolic," said Nicolas Florquin, a senior researcher at the Small Arms Survey. "The shape looks like the AK-74U Bin Laden had in the background of his videos. In some illicit markets, as in Lebanon, the AK-74U is nicknamed the Bin Laden."
Coulibaly could have bought the VZ58 legally in France with the right permit. Mr Florquin said: "He could have stolen it, borrowed it from a legal owner, or bought it on the black market."
Coulibaly also used a Skorpion, a Czech-made gun which stopped being manufactured in 1979 but is still common in the Balkans and among Europe's criminals.
Coulibaly's Tokarev is equally common. The Soviet Union made some two million of them. However, the Kouachi brothers each had an AKS-74 Kalashnikov, less common than its predecessor, the AK-47. Only Bulgaria and Romania of the Balkan nations have a history of making it.