At one point while Johnson and I talk, a BART conductor leans out the front window and shouts to Johnson, "Hey, you look familiar!" She replies, "I'm Oscar's mom."

On the last day of 2008, just hours before Grant died, he, Johnson and the rest of her family spent the day together. It was Johnson's birthday.

"That was the last time I was able to see Oscar. We had my birthday dinner together. We had gumbo," Johnson says quietly as she remembers Grant filling his bowl multiple times with her homemade gumbo.

Shortly after dinner, Grant headed into San Francisco with his friends. Johnson remembers him wanting to drive, but she pleaded with him to take BART because it would be safer.

Johnson looks at a corner toward the end of the platform, not more than 10 feet from where we are sitting.

"And here on this very platform right over there, in this very space, he ended up losing his life," she says.

For people who have lost a loved one to violence, going to the spot where they died can often hit too close to home. But for Johnson, it's different.

"It’s a healing and a hurting at the same time," she says. "I know that Oscar is here with me, and he encourages me to keep on going because that is what Oscar would have wanted."

Now Johnson spends her time in the community, where she advocates for at-risk youth and promotes justice for people like her son who have been killed by law enforcement. She heads the Oscar Grant Foundation, a nonprofit that supports young teens to reduce high school attrition, teen crime and teen pregnancy.

Johnson says she meets annually with other mothers who have lost families to police violence: Gwen Carr, mother of Eric Garner and grandmother of Erica Garner; Sybrina Fulton, mother of Trayvon Martin; and Lesley McSpadden, mother of Michael Brown.

"His legacy will always be here with us. I will always encourage others to love their family because we don't know what tomorrow will hold for us," she says as her eyes well up with tears.

The fliers that she was handing out earlier are invitations to the ninth annual vigil for Grant at the Fruitvale BART Station on New Year's Day. Johnson will be there along, with Grant's 13-year-old daughter, Tatiana Grant. Johnson says community leaders, faith leaders and activists will be in attendance to promote the theme "Speak Up and Judge Fairly."

"We want you to speak up about the injustices within our community," Johnson says. "We are asking our government and our police officers and our judges and courthouses to judge fairly."

In 2010, Johannes Mehserle was convicted of involuntary manslaughter by a jury that also considered the more serious charges of voluntary manslaughter and second-degree murder. He was given credit for good conduct in jail and released after serving about half of his two-year sentence.

Johnson says carrying on her son's legacy is what keeps her hopeful.

"Oscar was an encourager," she says. "If you were feeling down, he would try to say the very thing to make you laugh, to make you not dwell on the hurt or pain you would feel."

She says that's the kind of person she wants to be to those who have lost family members to police violence.