Revere's depiction of the Boston Massacre was full of inaccuracies which leads me to believe it was created primarily for propaganda purposes.  First of all the picture makes it look like it was day time when the events acctually occured.  In fact it was 9:00pm in early March.  I doubt it was the street lights that illuminated the area.  Also, eye witnesses indicated there was snow on the ground and in fact the colonists were throwing showballs or chunks of ice at the British soldiers.  The depiction doesn't even show the colonists with clubs which were reported by the eye witnesses.  Finally, the picture shows Prescott behind the soldiers rather than in front as the eye witness accounts indicate.  All this information was available at the time so my guess is that Revere wasn't trying all that hard to be accurate.  He was more interested in making a point.