FBI: Explosives with notes threatening Verizon, AT&T found outside 2 Michigan cellphone stores

Someone left explosives and threatening notes outside two northern Michigan cellphone stores Thursday, prompting an FBI investigation.

The explosives were found inside USPS Priority Mail boxes sealed with black duct tape at stores in Sault Ste. Marie and Cheboygan. 

Authorities said the boxes had "CMT" written on them. There were threatening notes signed by "HJ" or "Handcuff Johnny" and addressed to Verizon and AT&T on the top of each box. 

The FBI and Michigan State Police believe these explosives are related to a series of letters discovered at telecommunications tower sites in the UP last month. The letters claimed  to be from the "Coalition for Moral Telecommunications." They made specific demands to the companies.

Anyone with information is asked to contact the FBI at 1-800-CALL-FBI or tips.fbi.gov.