As the filming of police killing unarmed African Americans has led to a wave of protests and calls for reform across the US, one aspect of the controversy has received little attention: the after-the-fact targeting, harassment, and arrest of many of those who recorded and publicized the killings in the first place.

Today, dozens of Oscar-winning and nominated documentary film-makers – including Laura Poitras, Alex Gibney and many others – published an open letter calling on their fellow film-makers to defend these brave citizen journalists and activists who are now seemingly targets of the police themselves. They are also demanding the justice department investigate the disturbing pattern of police abuse.

With little media attention, many of the people who filmed the most notorious police killings in the last two years have subsequently been stalked and arrested by the very police departments that they filmed. The two most recent killings that made headlines around the country – the death of Alton Sterling in Louisiana and Philando Castile in Minnesota – are only the latest examples. Taken together, the pattern is startling, and for the first time, the letter’s organizer, director David Felix Sutcliffe, has catalogued many of these incidents in one place.

After Castile’s fiance, Diamond Reynolds, filmed his dying moments on Facebook Live, she was cuffed, locked in a police car, separated from her child and held in police custody for eight hours. “My daughter will be forever scarred by what the police did,” she said afterwards. “They took me to jail. They didn’t feed us. They put me in a room and separated me from my child. They treated me like a prisoner.”

The owner of the convenience store outside where Sterling was killed, Abdullah Muflahi, was also arrested by police, had his cellphone footage confiscated without a warrant, and was also locked up for four hours in the back of a police car. He has filed a lawsuit against the police officers involved.

Chris LeDay, one of the first to post the video of Sterling’s death that caused it go viral, was surrounding by military police at his job the next day. As Sutcliffe described: “They not only handcuffed him, but also placed him in leg-shackles. He was delivered to a local jail, stripped of his clothing, ordered to wear an orange jumpsuit, locked in a cell, and told he’d have to wait seven days before seeing a judge.”

The list goes on. The man who filmed the Eric Garner murder, Ramsey Orta, accused the NYPD of stalking him afterwards and filming him. He was eventually arrested multiple times and recently pled guilty to weapons charges. Two weeks after Kevin Moore filmed part of the Freddie Gray incident, he was arrested while police pointed assault rifles at him (no charges were filed). He later told Vice News: “Police sit outside my son’s school. And they ride past taunting me with their phones up.”

Taken together, these incidents show a clear pattern of abuse and this should be a controversy in and of itself. Almost all police departments have been forced to concede in recent years that everyone in the United States has a first amendment right to record the police in public spaces. So while they can’t prosecute people for filming them killing unarmed civilians, it’s clear that police departments are using their position of power to intimidate those who have led to more scrutiny of police and to send a message to those who may attempt to do so in the future.

Sutcliffe, who co-directed the documentary (T)error that relied on unauthorized footage of entrapment stings by the FBI, wrote that he was inspired to organize the campaign because of the fear of government retribution nearly led to the film being suppressed. “Fortunately,” he wrote, “the documentary community rallied to defend us, and denounced the threat posed by our circumstances, not just to the fate of our film but to free speech and a free press.”

Those who record and publicize police violence deserve the same. But more than that, they deserve to have their first amendment rights protected – not just as they film, but afterwards – to prevent the next person from being frightened off before they turn on their camera.