Teenager Kaylynn Gilbert, who begged policeman Derek Chauvin to stop kneeling on George Floyd’s neck a year ago today, thinks the officer tried to stop witnesses knowing the dad-of-five had died at the scene.

Giving her first interview about the murder, she says she believes that as the minutes went by, Chauvin realized he had killed Mr. Floyd.

Kaylynn, 17, thinks the policeman feared if he had got up off the victim it would have been obvious he was dead, and witnesses might have turned violent.

Kaylynn, whose video of the killing and evidence in court helped to convict Chauvin of murder, said: “I believe Derek stayed on his neck for so long because he knew he was dead.

“If he would’ve got up before the ambulance arrived, it would have escalated. Everybody would have known there and then George was dead… The police would have killed someone else.”

As she tearfully watches her video of the killing, she adds: “It doesn’t make sense why he would stay on top of him, especially after George was unconscious.

“A cop doesn’t have any reason to be applying pressure to them when they’re handcuffed. He knew what he was doing. I understood what he was doing.

“I had a gut feeling George was dead because of how the paramedics later lifted him up and how they were reacting.

“When I watch my video back, I can see that when the ambulance crew arrived they went to check his pulse, it was clear they couldn’t find one.”

“They then took their time to get the [stretcher]. Unbelievably, Derek was still on his neck. The ambulance crew had to signal to him to get off him.

“It was like they were saying ‘get up off of him – he’s dead. It was murder, pure and simple.”

Mr. Floyd, 46, was arrested on suspicion of trying to use a counterfeit $20 bill in a shop in the US city of Minneapolis.

He was placed on the ground in the street and Chauvin put his knee on the dad’s neck for over nine minutes.

Mr. Floyd was unconscious for around three of those minutes.

Kaylynn and her best friend Alyssa Funari arrived in a car as Mr. Floyd was arrested.

Kaylynn, who suffers from anxiety and who stayed in the vehicle while her pal headed to a shop to buy a phone cable, could hear the commotion nearby and told Alyssa “take my phone” to film the arrest because she had a feeling something wasn’t right.

As she watched from the car, she could hear her friend becoming increasingly distressed by what she was seeing, and then got out of the vehicle herself.

Kaylynn said: “At the time, I knew George needed help, but I didn’t know then Chauvin was killing him.”

Mr. Floyd had been telling officers: “I can’t breathe.”

Kaylynn immediately moved closer to Mr. Floyd, at one point being only a few feet away, begging the officer to get off his neck. Chauvin then threatened her with his pepper spray.

She says: “I really think if me or anyone else there would have continued to move forward to challenge the police, somebody else would have been killed by them as it was getting so intense.”

Kaylynn again began trying to appeal to the officers. She adds: “I kept repeating myself. I was like, ‘Why are you guys still on top of him? He’s not doing anything wrong.” She says the officers checked Mr. Floyd for a pulse several times, but it seemed they could not find one.

She says his face had turned dark purple and that Mr. Floyd was dead by the time the ambulance arrived. Paramedics told the trial Mr. Floyd had no pulse when they got there. He was pronounced dead at the hospital.

Chauvin’s lawyers claimed in court that a sudden heart attack or a drug overdose was responsible for the death.

But the jury disagreed and the sacked officer was found guilty last month. The 45-year-old is due to be sentenced on June 25. Kaylynn says: “What gets me most is there were kids there.

“I’m a kid, but there was a nine-year-old there that witnessed that.

“And what? [Chauvin] didn’t see anything wrong with what he is doing? After so many people told him to get off him.” The killing sparked protests around the world.

On the first anniversary today, thousands of people are expected to attend a commemoration in Minneapolis and other events around the US. Some of his family are expected to attend a candlelight vigil at the spot where he was killed.

At the weekend, Mr. Floyd’s relatives and others who have lost loved ones during police encounters were joined by supporters in Minneapolis for a march

Hundreds of people gathered in front of the court where Chauvin was convicted, many carrying signs with pictures of Mr. Floyd and other black men killed by police officers.

Mr. Floyd’s sister Bridgett told the crowd: “It has been a long year… a painful year.”

Before the trial, the family was awarded a record £19million settlement from the city.

Kaylynn was one of nine witnesses – including Charles McMillian, 61, the first bystander to see the fatal arrest – to give evidence at the trial

The teenager, who grew up in the tough southern area of Minneapolis where Mr Floyd was killed, now hopes to turn her harrowing ordeal into something positive.

It has inspired her to dream of becoming a defence lawyer.

Coming from a deprived background, struggling to get by and being homeless until a few months ago, Kaylynn is hopeful she can become the first person in her family to go to university.

“Given the struggles my family have faced and witnessing George’s death, I’d like to become an attorney to help others,” she says.

“I hope that for others, he did not die in vain.”

She said she and other residents of Minneapolis are “extremely grateful” to people in Britain who now campaign to bring about change in Mr. Floyd’s name.

She adds: “I think that’s amazing how everyone’s coming together after such a loss, particularly young people like me.

“But if we want to change, we gotta be the change… become that doctor, become that police officer.

“Follow your dreams – be the difference in the system.

We can’t control the bad people, but it all starts with one person being a good person and speaking up.

“That’s all it took with George Floyd. That one, that old man, Charles McMillian.

“He was the first person there. It just took one person to start with, and then more people came up and started speaking.