SALEM – A Lynn man who police say robbed St. Jean’s Credit Union four times over a two-month span remains held on a high bail of $50,000 cash at the Middleton Jail.Derek Christiansen, 34, of 113 Franklin St., #5, Lynn, appeared Wednesday morning in Salem Superior Court for his arraignment pleading innocent to four counts of unarmed robbery, crimes that could net him a life sentence in state prison.Judge David A. Lowy set the high bail as jointly recommended by the prosecutor and defense, agreeing that the defense may seek a bail review at another court date.Assistant District Attorney Jean M. Curran said the charges stem from four incidents that began in February.On the late afternoon of Feb. 7, Christiansen reportedly walked into St. Jean’s Credit Union located at 527 Western Ave. in Lynn, handed a note to the teller demanding money and fled with $300.Then on March 5, he allegedly returned to the bank at about 8:30 a.m., passed a note again to the same female teller demanding cash, leaving the bank with about $900.On the morning of March 18, he apparently returned again to the bank wearing a gray hooded sweatshirt over his head, passed a note again, and fled with about $1,000 towards Franklin Street.Then on the afternoon of March 24 he allegedly returned again, wearing a baseball cap and fled with about $1,000.Christiansen was arrested the following day after a police officer recognized him from the video from one of the bank robberies.In each of the holdups, no weapon was displayed. All four notes were left behind in the bank and the robberies were captured on the surveillance videos.Christiansen has been deemed indigent, meaning he has no money to hire his own attorney, but must pay $150 towards the legal representation.Public defender Mark Schmidt will be his defense counsel.Christiansen is due back in court on June 16 for a pretrial conference.