CANTERBURY, England -- Three young women were being hunted by British police Thursday after an "elaborate hoax" involving dummy bombs shut down a city in southeastern England.

Detectives released CCTV images of the group they believe carried out a sophisticated plot in Canterbury, Kent and said the suspects could be planning something more serious.

The images show the women on what appears to be an innocent shopping trip in West London two weeks before the hoax devices caused a major security alert in the city on Aug. 26.

Police said that the group visited a cell phone store and purchased prepaid cell phones that were activated the day before the plot and have not been switched on since. The phones were used to contact police and the media.

One of the hoax devices was found in a changing room in a Marks & Spencer retail store. It contained a smoke grenade which was set off by a male suspect, who was captured on the store's CCTV.

The second device was disguised as a realistic pipe bomb and was left by a railway track.
Police were forced to evacuate the area and call in the army bomb squad.

"This is a very unusual case," Detective Chief Inspector Tom Richards, of Kent Police, said. "We believe those responsible are an organized group who had put serious and meticulous planning into committing these offenses, although at this time the motive behind the hoaxes is still unclear and no-one has claimed responsibility for them."

The detective admitted he and his colleagues are baffled by the plot and have ruled out nothing, including terrorism.

He added, "Following an extensive investigation, we have established that the bomb hoaxes appear to be a sophisticated criminal act with elaborate hoax devices guaranteed to cause considerable disruption and distress to the people and businesses in Canterbury and to the traveling public."