SALEM – A man caught in Lynn after threatening to blow up a Salem bank while stealing $579 in cash last February will be behind bars for up to eight years.In Salem Superior Court Friday, Robert P. Morneau, 35, last known address of 40 Beaver St., Salem, pleaded guilty to a charge of armed robbery.He was sentenced to serve not less than five years and not more than eight years in state prison by Judge Timothy Q. Feeley.On Feb. 11 a man walked into the Salem Five Cents Savings Bank branch located at 424 Essex St. in Salem, went up to a female teller, slammed his hands on the counter and began yelling that he would blow up the building with explosives if she didn’t turn over the money.The teller cleaned out her cash drawer and handed over $579 and the robber fled the scene.Authorities learned through a patrolman that the suspect might be Morneau.Lynn and Salem police arrested Morneau about a week later on Boston Street in Lynn.Bank employees and witnesses who saw the robber inside the bank identified Morneau as the holdup man.The judge credited Morneau the 271 days he has spent in jail awaiting trial on the case.Morneau was indicted by an Essex County grand jury in May 2009.