What should you do if you see police using excessive force? Legal experts say film it, just as bystanders did in George Floyd's death.

Darnella Frazier said filming George Floyd's death changed her life. Frazier's 9-year-old cousin said witnessing the incident made her "sad and kind of mad." Donald Williams said he called police on police because he thought what he had just seen was a murder.

As witnesses took the stand this week and the jury was shown cellphone video of Floyd's death in the trial of Derek Chauvin, the final moments of Floyd's life were once again thrust into the national spotlight.

But if it weren't for bystanders who stopped and filmed that day, the world might have never learned Floyd's name and the case against Chauvin could have been completely different, legal experts told USA TODAY. It highlights the importance of knowing what to do when encountering police abuse or excessive force, they say.

"People in the community video taped and were present which is why we know what happened on that day," said Tyler Crawford, director of mass defense at the National Lawyers Guild.

"I don't think the importance (of the video) can be overstated," added Puneet Cheema, manager of the NAACP Legal Defense and Educational Fund's Justice in Public Safety Project.

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In his opening statement, prosecutor Jerry Blackwell credited bystanders "from the broad spectrum of humanity."

"What they all had in common is they were going about their business, is that they saw something that was shocking to them, that was disturbing to them, and it made them stop and take note."

This image from a police body camera shows people gathering as former Minneapolis police officer Derek Chauvin was recorded pressing his knee on George Floyd's neck for several minutes as onlookers yelled at Chauvin to get off and Floyd saying that he couldn't breathe on May 25, 2020 in Minneapolis.

What should you do if you think you see police using excessive force?

If you think you are witnessing police abuse, stop if you feel comfortable, bear witness, try not escalate the situation and, if possible, film the encounter, according to Crawford and Cheema.

Simply stopping and watching is one of the best things a bystander can do because witnesses are called to testify often if a case goes to trial, Crawford said. They can provide a third-party account of what happened.

During protests, legal observers trained through a National Lawyers Guild program may be deployed to watch what happens. "Unsurprisingly, just the presence of legal observers has a chilling effect on law enforcement's willingness to engage in unconstitutional behavior," Crawford said.

Filming provides further corroboration. "Documenting what's happening is always a good idea. How many people have caught law enforcement in unconstitutional activities by video taping with cellphone what's happening," he added.

Cheema said, however, observers have to be cautious of their own safety given their own identities. A person's race, gender or legal status as a resident could factor into a person's decision to stop and bear witness to a police action. "It's understandable if folks need to protect their own safety," she said.

Standing at a distance and stating that you're within your legal rights to film in a public place can help prevent a bystander from escalating the situation, Crawford said.

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During the Chauvin trial, Blackwell, the prosecutor, said bystanders first tried to intercede by telling Chauvin and the other officers to stop. 

"When that didn't work, you can see any number of them pulled out their cameras to document what was happening, such that it would be memorialized, such that it would not be misrepresented, such that it could not be forgotten," he said.

Blackwell called the video evidence "helpful and meaningful" for the jury. "You can see it for yourself without lawyer talk."

In New York City, Steve Kohut is an organizer with Cop Watch, a program part of the grassroots group the Justice Committee that documents arrests and police interactions within communities.

Cop Watch was first created and implemented by the Black Panthers in the 1960s, but came to New York through various community groups in the 2000s, Kohut said.

The group regularly organizes patrols of citizen observers in neighborhoods throughout New York City where community members have indicated high occurrences of police misconduct and abuse, he said.

"We pull out a camera, document the incidents and let the person involved in the incident know we're there to help them," Kohut said. The biggest concern for those on Cop Watch is that "the person is treated respectfully and their rights are not violated," he said.

The point is not to stop a police interaction or interfere with an arrest, but rather to serve as an independent witness to ensure accountability if a person's rights were violated, Kohut said. "There are three sides to a story: My side, your side and the truth," he added.

What are your rights if you're experiencing police harassment or abuse?

Kohut said "you'd be surprised" how few people know their legal rights during a police encounter. "The first step of everything is know your rights," he added.

Civil rights organizations have published extensive guides on individuals' rights are during a police encounter – including the right to remain silent, to talk to an attorney before speaking with police, to refuse a search or ask to see a search warrant, and to ask if you are free to leave.

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If you are stopped by police and are worried of potential abuse:

►Ask if you are free to leave: Cheema said one should always ask if they are free to leave because it will establish whether police are seeking information from you or if they have reason to believe you might be connected to a crime.

►Know you can remain silent: It's still a good idea to be cooperative to prevent aggravating an officer, Cheema said, but know that you don't have to answer every question from an officer.

►Be mindful of how your actions may be perceived: "The one key you want to make sure that you are continually aware of is that you are not exacerbating the risk to yourself," Cheema said. 

There is a wide range of ways a person could face resisting or obstructing an arrest or disorderly conduct charges, she said.

"At the end of the day, police officers are human beings and if they feel threatened – either by someone doing something physical or someone who is video taping what they're doing – they can react in a number of ways that could threaten your physical health and safety," Crawford added.

►Film if you feel comfortable doing so: If no one else is around or filming, you are free to do so, too. It will provide corroboration for what you experience, and the act of filming is itself not accusing the officer of any wrongdoing, Crawford said.

"If you are being stopped in a car, it may be best to begin recording at the beginning of an interaction," Cheema said. "You just have to make sure that you're collecting and documenting as much as you can. … Even videos can't capture everything."

►Seek witnesses: A witness can also provide corroboration. Cheema said if you see someone you don't know who was nearby and are able to do so, try to get their name and contact information.

►Understand officers may lie: While legal rights provide "a framework" for protection in the criminal justice system, Crawford said "you have to understand that there are more fundamental dynamics at play that often have nothing do with what your rights are or are not." 

"Testilying" is a well-documented legal phenomenon in which police perjure themselves to justify their actions or ensure a conviction, he said. A New York Times report from 2018 found at least 25 cases in New York City over three years in which police likely lied.

►File a complaint: Anyone who believes they've experienced harassment or abuse has a number of options after the incident, too. Many police departments have internal affairs divisions that handle complaints. Cities may also have civilian review boards that provides independent oversight over a department.

A person can also initiative a civil suit against public officials, but the doctrine of qualified immunity shields often shields officials like police officers from personal liability in such cases, Crawford said.

Qualified immunity shields officials unless someone can prove their actions violated "clearly established" laws or rights. Crawford said the principle is "very difficult to overcome because it's so subjective," adding that it's one of the biggest barriers for those seeking justice in police abuse cases.