London attackers likely used simple, homemade bomb, plastic explosives

LONDON — The bombs that destroyed three London Underground cars and a double-decker bus were each lighter than 10 pounds and could be carried in a backpack, police said Friday. An explosives expert said they were likely crude homemade devices set off with a simple timer.

The bombs were probably made from simple, relatively easy-to-obtain plastic explosives, not the higher-grade military plastics like Semtex that would have killed far more people, said Andy Oppenheimer, a weapons expert who consults for Jane's Information Group.

"Any crook with ready cash could obtain this stuff if they knew where to look for it," said Alex Standish, the editor of Jane's Intelligence Digest.

Plastic explosives are readily available on the black market in the Czech Republic and other central and eastern European countries or through the Russian mafia, Standish said. Large amounts of plastic explosives untagged by the chemical markers that enable dogs to detect it are missing from Czech stocks, he added.

Police said the four bombs that hit the London transportation network on Thursday weighed less than 10 pounds each, small enough to be carried in a backpack. They were left on the floor of the Underground trains and either a seat or the floor of the No. 30 bus that was ripped apart in the Bloomsbury neighborhood, said Assistant Police Commissioner Andy Hayman.

Ten pounds is a relatively small bomb, although a blast's power depends more on the type of explosive than the amount. The 10 bombs that killed 191 people on commuter trains in Madrid, Spain last year averaged 22 pounds each; the bombs that killed 33 bystanders and 12 suicide attackers at five targets in Casablanca, Morocco, two years ago were 18 to 22 pounds each.

Hayman said investigators had so far obtained little detailed forensic information on the bombs. Their investigation has been hindered by the inaccessibility of one of the wrecked trains, 70 feet below street level, he said.

Bodies were still trapped in the mangled Picadilly line train between theKing's Cross and Russell Square stations, the site where at least 21 people were killed.

Rescuers got all the survivors out in the hours after the blast but decided not to go back to remove the dead or recover evidence until they can shore up the tunnel, which sustained structural damage and may be unsafe, said Sir Ian Blair, commissioner of London's Metropolitan Police.