This is the case back from New Year's, when a man named Oscar Grant was arrested and lying facedown on the platform when an officer shot him in the back, killing him.
Some hypothesized that the officer slipped, got nervous, maybe mistook his gun for his Taser. But a lot of protesters said it had to be murder. And now the DA agrees -- he's bringing a second-degree murder charge.
Hat Tip: Many thanks, You're A Mean Drunk R2D2!