Possible Clues:

• Secure telephone provided for the explosives expert
• Robber, easier to catch, given a month inside
• Thief using explosives
• Secure phone provided for explosives expert
• Criminal, not so bright, gets a month inside
• Criminal finally makes drop after a month
• Felon requiring secure phone
• Criminal who requires secure phone line
• Telephone unlikely to pose a risk for criminal
• One cracking secure phone?