A Dorchester man and a female Roxbury juvenile were arraigned Wednesday in a knife and bleach attack that began on a MBTA bus and continued outside the vehicle in Dorchester on Dec. 6, according to the Suffolk district attorney’s office. Jahmahl Galloway allegedly stabbed one victim in the head, and the juvenile then allegedly threw bleach at the victim, another person, and at Galloway, the district attorney’s office said in a statement. Galloway and the female fled, but were later identified from surveillance footage, prosecutors said. Conley’s office said the two were charged in Dorchester District Court with several counts of assault and battery with a deadly weapon. They pleaded not guilty.