I think I may also have found the reason that Boston is pushing for the knife control law. In the FBI's UCI for 2010 they took a black eye for a murder rate increase of 47% (50 to 73 homicides) while almost everybody else is decreasing.
Could it be that many places are now supporting concealed handgun carry and self protection while Boston is not? Those other places see their crime rates going down, but Bostons murders are going way up.