MBTA Transit Police said they had help Monday arresting a Roxbury man wanted on four warrants, help from the suspect himself. John Monroe, 32, was apprehended at the Quincy Center Red Line station around 8:20 pm. after he drew the attention of police. Monroe, Transit police said, stood in the open doorway of a Red Line car, with one foot inside and the other on the platform. When police asked him to get on the train or step onto the platform and when the station attendant used an intercom to broadcast a request that he move, Monroe allegedly was immobile. Police took Monroe into custody and discovered that the Fisher Avenue resident had four outstanding warrants.