From the U.S. Code Online via GPO Access
{wais.access.gpo.gov} said:
(m) The flag, when flown at half-staff, should be first hoisted to
the peak for an instant and then lowered to the half-staff position. The
flag should be again raised to the peak before it is lowered for the
day. On Memorial Day the flag should be displayed at half-staff until
noon only, then raised to the top of the staff. By order of the
President, the flag shall be flown at half-staff upon the death of
principal figures of the United States Government and the Governor of a
State, territory, or possession, as a mark of respect to their memory.
In the event of the death of other officials or foreign dignitaries, the
flag is to be displayed at half-staff according to Presidential
instructions or orders, or in accordance with recognized customs or
practices not inconsistent with law. In the event of the death of a
present or former official of the government of any State, territory, or
possession of the United States, the Governor of that State, territory,
or possession may proclaim that the National flag shall be flown at
half-staff. The flag shall be flown at half-staff 30 days from the death
of the President or a former President; 10 days from the day of death of
the Vice President, the Chief Justice or a retired Chief Justice of the
United States, or the Speaker of the House of Representatives; from the
day of death until interment of an Associate Justice of the Supreme
Court, a Secretary of an executive or military department, a former Vice
President, or the Governor of a State, territory, or possession; and on
the day of death and the following day for a Member of Congress. The
flag shall be flown at half-staff on Peace Officers Memorial Day, unless
that day is also Armed Forces Day. As used in this subsection--
(1) the term ``half-staff'' means the position of the flag when
it is one-half the distance between the top and bottom of the staff;
(2) the term ``executive or military department'' means any
agency listed under sections 101 and 102 of title 5, United States
Code; and
(3) the term ``Member of Congress'' means a Senator, a
Representative, a Delegate, or the Resident Commissioner from Puerto
Rico.