Before Trayvon Martin donned a hoodie, before the “hands up don’t shoot” protests over the death of Michael Brown, before Eric Garner said he could not breathe, Oscar Grant was belly-down on a BART train station platform.

Ten years ago New Year’s Day, BART police Officer Johannes Mehserle fired a shot into the back of Grant, killing the 22-year-old Hayward man — and ushering in an era of awareness and anger over police shootings, especially those involving black men at the hands of white officers.

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Seeing Grant pinned to the ground exposed his vulnerability to police in the moments leading to his death and begged the question, “Why did this have to happen?” said Robert Weisberg, a professor of criminal justice at Stanford University. For a society asked to trust its police officers, the footage was a jarring contradiction that planted a seed of doubt.

“The Grant shooting raised public awareness and public skepticism about police,” he said.

“The Ferguson event is what turned it into not only a national but an international phenomenon, in the fact that the whole world was watching,” he said, referring to the massive protests in a St. Louis suburb after an unarmed black teenager was killed by a white officer who was later cleared. Michael Brown’s shooting was not recorded.