Third, there’s still so much that the public doesn’t know and much that is left to police discretion. This already-bleak anniversary is made darker by the mysterious death of Sandra Bland. The 28-year-old black woman from Chicago was on driving to Texas for a new job when she was stopped by police near Houston for failing to use a blinker. During the traffic stop, she was eventually arrested in Waller County by a state trooper for assaulting a public officer, arraigned, and sent to jail on $5,000 bail. On Monday, she was found dead in her cell of what the sheriff says is self-inflicted asphyxiation.

Bland’s family rejects that—they don’t believe that she would have hurt herself, noting that she seemed in high spirits even after her arrest on Friday, and saying it’s generally out of character for her. The FBI has now joined the investigation, and a video has surfaced that reportedly shows part of the arrest. But by the time the clip begins, an officer is already physically subduing Bland. There’s still a great deal that is unknown about her arrest and death. Are stops for failing to use blinkers routine in Waller County, or used as pretexts for pulling over certain kinds of drivers? What happened between the driver and the officer? Was Bland the aggressor, as police have it, or was the officer at fault? Are there other recordings of the stop? Did the police act appropriately? What happened between Friday afternoon and Monday morning as Bland waited in her cell?

Many of these things may be unknowable, and others will emerge over the coming days and weeks. What’s clear from the start is that a traffic stop for failing to signal a lane change, involving an African-American woman with no apparent criminal record, somehow escalated to a physical altercation between the officer and the driver and ended with a young woman dead in a county jail cell. Eric Garner’s death one year ago may have been the beginning of Americans paying attention to police violence against people of color, but Bland’s death shows why the anniversary doesn’t offer any closure.