Boston police arrested a man suspected of trying to rob a Citizens Bank branch at 2343 Washington St. in Roxbury on Saturday, police said in a blog post. Marco Willis, 40, of Boston was arrested less than three hours after the alleged robbery attempt. According to the police blog, a man entered the bank at about 11:30 a.m. and held up a deposit slip with “No dye pack” written on it. The manager asked the man to wait and activated an alarm. The man left the bank with no money. At about 2:14 p.m., an officer saw Willis, who fit the suspect’s description, walking about a half-mile from the bank. The officer arrested Willis, who was charged with attempted unarmed bank robbery.