Protesting police killings

People take part in a march against police violence, in New York December 13, 2014.   (Eduardo Munoz / Reuters)

People take part in a march against police violence in New York December 13, 2014.   (Eduardo Munoz / Reuters)

Demonstrators hold signs during a rally on Pennsylvania Avenue during the National Action Network National March Against Police Violence in Washington December 13, 2014.  (Joshua Roberts / Reuters)

Lesley McSpadden, mother of police shooting victim Michael Brown helps lead a rally and march against police brutality and the killing of unarmed black men by police in the nation’s capital, December 13, 2014.  (Chip Somodevilla / Getty Images)

Demonstrators march down Pennsylvania Avenue during the National Action Network National March Against Police Violence in Washington December 13, 2014.   (Joshua Roberts / Reuters)

Thousands of people descended on Washington to demand justice on December 13, 2014 for black men who have died at the hands of white police officers, the latest in weeks of demonstrations across the United States.  (Brendan Smialowski / AFP/Getty Images)

A protester holds a sign during a march in Washington December 13, 2014.  (Brendan Smialowski / AFP/Getty Images)

Demonstrators march down Pennsylvania Avenue during the National Action Network National March Against Police Violence in Washington December 13, 2014.   (Joshua Roberts / Reuters)

Demonstrators march to Capitol Hill in a protest against police violence organized by the National Action Network in Washington December 13, 2014.  (James Lawler Duggan / Reuters)

Al Sharpton marches with family members of Eric Garner, Michael Brown, Tamir Rice and Trayvon Martin to Capitol Hill in a protest against police violence organized by the National Action Network in Washington December 13, 2014.   (James Lawler Duggan / Reuters)

Demonstrators march during the National Action Network National March Against Police Violence in Washington December 13, 2014.  (Joshua Roberts / Reuters)

Police officers scuffle with protesters during a demonstration against recent grand jury decisions not to indict police officers in the deaths of Michael Brown and Eric Garner, in Boston, Massachusetts.  (Brian Snyder / Reuters)

Protesters chant during a demonstration against recent grand jury decisions not to indict police officers in the deaths of Michael Brown and Eric Garner, in Boston, Massachusetts.  (Brian Snyder / Reuters)

A woman with “#NoJusticeNoPeace” written on the side of her head marches during a demonstration against recent grand jury decisions not to indict police officers in the deaths of Michael Brown and Eric Garner, in Boston, Massachusetts December 13, 2014. REUTERS/Brian Snyder (UNITED STATES - Tags: CIVIL UNREST CRIME LAW SOCIETY) ** Usable by BS, CT, DP, FL, HC, MC, OS, HOY, CGT and CCT **  (Brian Snyder / Reuters)