Three mobiles used in Canterbury bomb hoaxes
A least three pay-as-you-go mobile phones were used by a group that caused a major alert in Canterbury with two bomb hoaxes, police believe.
Trains were halted and parts of the city cleared while police investigated the incidents, on 26 August.
Kent Police said the phones, used by the group to contact each other and the media, were bought in a mobile phone shop in London, on 14 August.
The force has issued CCTV images of three women who bought the phones.
The phones, which were bought in the West End, were not activated until 25 August, in south-east London.
Detectives said the women may have vital information that could help their investigation.
Emergency services were first alerted to the hoaxes when a call was received by Kent Police main control room at 16:20 BST, informing them of a suspect package near the railway line off Old Dover Road.
About an hour later, they were called to a suspected fire in the baby changing area of Marks and Spencer in Whitefriars Shopping Centre, where a second suspect package was found.
The package at Old Dover Road was then confirmed as a hoax device.
A smoke grenade was found to have been activated in Marks and Spencer, which police said was a sophisticated device designed to cause maximum disruption.
Police have previously issued CCTV images of a main seen in the store shortly before the alarm was raised.
The images show a man carrying a blue and black rucksack, a baseball hat and cycling gear.
It is believed the hoaxers could be from London or anywhere in the UK.
"This is a very unusual case and we believe those responsible are an organised group who had put serious and meticulous planning into committing these offences," said Det Chief Insp Tom Richards.
"At this time the motive behind the hoaxes is still unclear and no-one has claimed responsibility for them.
"I really want to appeal to the public to help us identify the people in the CCTV images.
"I would especially appeal to the women who were in the phone shop to get in touch."
The investigation is to be featured on Crimewatch on BBC1 at 21:00 GMT on Thursday.