A husband and wife from Essex who have been missing for more than a year were abducted and murdered by a random stranger, and a suspect is in custody in another state on other charges, state and federal authorities said Friday. Officials would not release the name of the person believed to have killed Bill and Lorraine Currier, who were last seen leaving their Burlington jobs on June 8, 2011. Authorities also would not say where that person is in custody or on what charges. State and federal officials said they expect that the suspect will be charged in the Curriers’ deaths, but they gave no indication when that would happen. ‘‘The public does have a right to know,’’ said Chittenden County State’s Attorney T.J. Donovan. ‘‘At this time, for a number of reasons, it’s not the appropriate time, but I think the purpose of today was to inform the public, to make that declaration that the Curriers were in fact murdered, that it was a random act, and that we believe the person responsible is in custody.’’