BOSTON, Nov. 7, 2007—Suffolk County District Attorney Daniel F. Conley and Boston Police Commissioner Edward Davis today announced the arrest of a suspect in the April homicide of Frank Dillon in East Boston.VICTOR ROSARIO, 20 (D.O.B. 9/2/87), of East Boston was identified during the course of an extensive seven-month investigation in the Suffolk County Special Grand Jury. Based on evidence developed in that ongoing probe, Boston Police on Monday obtained a warrant for Rosario’s arrest for the crime of manslaughter; this morning, they took him into custody in New Bedford [with the assistance of New Bedford and State Police]. Rosario’s arrest in the course of a joint investigation by Boston Police homicide detectives and Suffolk County homicide prosecutors makes him the sixth such suspect to be arrested in less than three weeks. On the night of April 23, Boston Police assigned to District A-7 (East Boston) responded to a call for a person shot at 44 Marion St. On arrival, they observed Dillon suffering from severe trauma to the head and another man, later identified as Rosario, suffering from a gunshot wound; both were transported to Massachusetts General Hospital. Dillon was treated for life-threatening injuries but succumbed to those injuries on April 27. Rosario is expected to be arraigned this afternoon in the East Boston Division of the Boston Municipal Court Department.