By Paul de Bendern
HELSINKI (Reuters) - Police say they are questioning two teenagers about an Internet chat room on bomb-making used by a chemistry student suspected of detonating a device which killed seven people in a Finnish shopping mall.
The National Bureau of Investigation (NBI) had earlier said it had detained two youths on Monday afternoon and later released one of them. It has now rearrested the youth who had been released.
"I can confirm we have two people in custody. It relates to the Internet chat room," NBI Inspector Rabbe von Hertzen told Reuters on Tuesday. "It (the second youth) was the same person that was previously detained."
NBI Deputy Chief Jari Liukku earlier told Reuters that police believed the pair had given advice about bomb-making over the Internet.
The NBI said they did not believe the detained teenagers helped carry out the bombing, which killed prime suspect Petri Gerdt and six others, but rather that they could have helped him in some way to build the bomb.
"We still have to find what the involvement could be. There is a lot of information to go through," Liukku said.
The home-made explosive, weighing up to three kg (6.6 lb) and packed with metal shards, went off during peak shopping hours on Friday evening in one of Finland's largest malls in Vantaa, the quiet Helsinki suburb where 19-year-old Gerdt lived.
Police said they did not know Gerdt's motive.
Tuesday was declared a day of mourning in the relatively crime-free country, which was stunned by the bombing. Flags were flown at half-mast and some official buildings were closed.
DO-IT-YOURSELF BOMB CHAT SITE
Liukku said the unnamed suspects were connected to an Internet chat room, which police believe Gerdt used to exchange ideas on bomb-making, explosives and its effects.
The Finnish chat room "Forum for home chemistry" has since been shut down by authorities and its host, who called himself Einstein, told Finnish YLE national broadcaster the site was not used to plan an attack.
Finnish tabloid Ilta-Sanomat said 17-year-old Einstein had been detained for questioning. Police declined to comment.
Police have not been able to pin-point how the bomb was made but said the explosive cocktail contained ammonium nitrate, a fertiliser used in the fatal 1995 Oklahoma City bombing.
Rolf Strandberg at Forcit, a Finnish firm making explosives for the military, said: "It's quite easy to make a bomb if you can get ammonium nitrate. These different nitrates are available."
Police found evidence at the home of Gerdt, including a computer and information on bomb making, that linked him to the crime and pointed them to chat rooms and other online sites.
Police said surveillance cameras and witnesses saw Gerdt arriving alone to the mall 20 minutes before the bomb exploded. They said he had visited the mall, just a few hundred metres (yards) from his college, the day before as well.
Gerdt used the alias RC in the Finnish chat room but gave no clear clues to a planned bomb attack.
"I have not taken part in any larger accidents, but once I dreamt that a police car drove to the site of the explosion, but luckily I was already floating to other places," RC wrote on the Web site.
RC also quoted lyrics from dead U.S. rapper Tupac Shakur, saying: "I ain't a killer but don't push me. Revenge is like the sweetest thing."
Fellow students said Gerdt was an introvert but polite, had few friends, liked laboratory classes and basketball.
