Jennifer Coffindaffer, a retired FBI agent, has put forward a dramatic 10-step plan she says could help crack the Nancy Guthrie kidnapping case, as the search for Savannah Guthrie's mother stretches nearly five months after her abduction from Tucson, Arizona, on 1 February. Her most eye-catching suggestion is a Bitcoin sting aimed at the ransom trail, alongside a renewed push to identify the masked figure known as 'Porch Guy'. Retired FBI Agent …