Terror suspects 'were tipped off'

BERLIN, Germany (CNN) -- The three terror suspects arrested last week in Germany may have sped up their bombing plot after a loud-talking police officer inadvertently alerted them that they were on a federal watch list, an unnamed source with knowledge of the investigation told CNN.

The men were stopped by a traffic officer in the weeks prior to their arrest last Tuesday. The traffic stop was described by the head of Germany's Federal Criminal Investigation Office, Joerg Ziercke, as "a setback for the group."

But it may have also been a boon for the suspects, who had been under surveillance for over six months.

Federal investigators had bugged the vehicle carrying the suspects during the traffic stop and could hear one of the police officers loudly exclaim that the men were on a federal watch list, the source said.

Days later, the men were observed mixing a massive amount of explosive materials that German authorities said could have resulted in a stronger explosion than the terror attacks in Madrid in 2004 and London in 2005.

At that point, investigators moved in and arrested the men at a rental house in west-central Germany.

A spokesman for the federal prosecutor's office said the suspects had been given a deadline to carry out the attack, possibly by the end of September, but it was not clear if they had sped up their plot to meet a deadline or because they learned that they were on the government's watch list.

The men -- two German converts to Islam and a Turk -- trained at Islamic Jihad Union camps in northern Pakistan, Ziercke announced Friday. He said their terror plot, which was aimed at American military installations and other Western targets in Germany, was initially uncovered after U.S. intelligence officials alerted German authorities.

German politicians are debating whether to make it illegal for citizens to attend terrorist training camps in Pakistan, but Germany Justice Minister Brigitte Zypries said that is not possible.

"It's very difficult to automatically make visits to training camps a crime because the person that has been there hasn't actually hurt anybody yet," she said. "We can't punish someone who hasn't committed a crime yet."

For the past three months, German authorities have been trying to track down a group of 10 to 15 people from Germany, or of German origin, who attended terrorist training camps in Pakistan in the past year, German Interior Ministry spokesman Christian Sachs told CNN.

They are not necessarily linked to the three arrested last week, nor were they definitively part of the Islamic Jihad Union terror cell in Germany, he said.

There are about 50 suspects inside and outside Germany that are part of the ongoing investigation, Sachs said.

The three suspects had amassed 1,500 pounds of hydrogen peroxide to use for making bombs, which would have the effect of 500 kilograms (1,100 pounds) of TNT, German authorities said. They also possessed several sophisticated detonators that the unnamed source said came from Syria.

Last week, Sachs said German police believe the detonators were brought to Germany in a "conspirative" way. The remaining bombing equipment was purchased in Germany, he said.

The detonators were types that can be used in a military device, and which are difficult to obtain, more precise and can inflict more casualties than lower-grade detonators, according to a counterterrorism source in Frankfurt with knowledge of the plot.

In addition, supporters of the suspects rented two vans in France and brought them into Germany as part of the plot, a spokesman for the federal prosecutor's office said. E-mail to a friend

CNN's Diana Magnay and Frederik Pleitgen in Berlin contributed to this report.

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