“If you have a building site and you plan to use 10KG of explosives, who can check if you are only using nine and selling the tenth kilo?” Malmö police chief Stefan Sinteus told TT.
“We are seeing a tendency to use more commercial explosives than before. We have, for example, no hand grenades left, and we see that the number of bangers has reduced. But we see plastic explosive.”
Jan Johansson, chief executive of Bergsprängningsentreprenörerna, the trade body representing explosives engineers in Sweden, admitted that companies were failing to keep a proper record of explosives on site.
“Every company should keep a register over all the explosives they have up until the time that they are used,” he said.
“Theoretically, it should be very simple to check if anything has disappeared. But that's not how it works in the real world. This register doesn't always function at 100 percent.”
- Stockholm blast 'one of the most powerful explosions' in the capital
- Swedish police reveal latest move to crack down on gang crime
- Swedish police chief: No international equivalent to Sweden's wave of bombings
After this week's explosions in Stockholm and Norrköping, Mikael Damberg, Sweden's interior minister, called a meeting bringing together government agencies with experts from the building sector.
“Not all [building firms] have the secure storage that is required. And they also probably don't always report it if something is stolen, as they they themselves might be suspected of committing a crime,” said Bo Janzon, a weapons expert at the Swedish Defence Research Agency.
He said it was also quite likely that people on building sites sold a portion of the explosives.
“You are supposed to keep a proper record, but because this substance probably has a value on the black market, you might expect individuals to make a little extra by selling it on the side.”
Part of the problem, argued Janzon's colleague Henric Östman, was that the rules over who on a building site could use explosives were so loose.
“There is one person in every company, the one who has overall responsibility, who you do a background search and check up on, but it's not necessarily that person who will then deal with the explosive material. That's an obvious gap.”
“It's strange that there isn't any requirement to make a registry of employees. Big companies which have a huge number of staff, are hiring people willy nilly.”
Lorens van Dam, an expert at the Swedish Civil Contingencies Agency, said that the rules requiring local municipalities to give permissions for the use of explosives were also not fully effective.
“It is sort of self evident that a municipal official would neither have the knowledge or ability to give out such permissions in a proper way. That's something that needs tightening up.”
Swedish police have called for explosives to be marked in some way so that you can trace the origin of the explosives used even after its been detonated.
“This has been discussed in the past but not carried out,” Östman said. “But if it can help police in their investigations, it is something that would be possible to do from a technical and scientific standpoint.”
Such measures would probably need to be taken at the EU level, he added, as most manufacturers of plastic explosive are outside of Sweden.