Families of Michael Brown, Eric Garner, Tamir Rice to march to Capitol

A week of marches across the country to protest excessive force by police culminates Saturday in Washington.

On Friday night, hundreds of demonstrators marched through Cambridge, Massachusetts. They staged "die-ins" in three of the city's biggest public squares.

The largest demonstration is expected in the nation's capital Saturday afternoon. Thousands of protesters will assemble in Freedom Plaza, just a block from the White House, for the start of the "Justice For All" march.

CBS News' Mark Albert reports the event, which is scheduled to last more than three hours, brings together several families united in grief.

From medical students at Yale to demonstrators blocking an interstate in Berkeley, California, and even in London, demonstrators this week have been protesting deadly use-of-force by police, primarily against African-American men.

The movement's flashpoint: the Aug. 9 death of Michael Brown in Ferguson, Missouri. Now, Brown's parents will walk side by side Saturday with two other families whose sons died in encounters with police: Tamir Rice, the 12-year-old who was shot to death in November by a Cleveland officer after holding a pellet gun, and Eric Garner, who died in July after a New York City police officer put an arm around Garner's throat.

Garner's widow, Esaw, spoke with "CBS This Morning" last week.

"I appreciate everyone that's out there marching for my husband because had it not been for the tape, for the people, for Reverend Al (Sharpton) putting it out there he would've just been another black man killed, and it would've been over," she said. "This way, his name will be remembered."

Saturday's march, organized by Sharpton's National Action Network, walks the mile to the U.S. Capitol.

It was on the Capitol steps where, just 48 hours earlier, about a hundred congressional staffers gathered in protest, adopting the "hands up, don't shoot" gesture.

The Department of Justice has launched civil-rights investigations into the deaths of Brown and Garner.

Brown's parents have launched a Change.org petition calling for police body cameras nationwide.