Among those lessons are:
3.However, where effective and modern firearms are not readily available (As in such "Blue States" as Massachusetts), such violent persons will gravitate to improvised weapons---Such as bombs;
4. There are many WMD which are inexpensive AND do not require the technical expertise demonstrated by Timothy McVeigh, the"9/11" supports of Islam and, today's Boston Bomber(s).
I might note that Mr. Obama's initial reluctance to call the new "Boston Massacre" Terrorism might be his wish to avoid the reasonable association of such terrorism with Islam, which is the source of the great majority of non-state (And, some state as by Iran) terrorism in this world. If the critters responsible for this Boston bombing should happen to be from some other ideology, the last fact should not be forgotten.
Those responsible waged war against the USA! If citizens, they should be charged with TREASON and tried before such a fair,effective, fair and efficient Military Commission as dealt with those who plotted the murder of President Lincoln; . If foreign, they should be tried by the like courts martial as dealt with the Nazi saboteurs who landed in the USA during World War-II.