A court has been examining CCTV footage of George Floyd taken shortly before his death, as the murder trial of former police officer Derek Chauvin enters its third day.

The footage provides the first glimpse of Mr Floyd’s actions inside a grocery store, where he is alleged to have used a counterfeit $20 note.

Shop employee Christopher Martin is the latest witness to take the stand.

Mr Floyd’s death in May sparked global protests about racism and policing.

Mr Chauvin was filmed pressing his knee on Mr Floyd’s neck for more than nine minutes before he died.

The 45-year-old denies charges of murder and manslaughter. Defence lawyers have indicated they will argue that 46-year-old Mr Floyd died of an overdose.

Christopher Martin, 19, told the court on Wednesday he briefly interacted with Mr Floyd as a customer inside Cup Foods shortly before his arrest.

He said he “appeared to be high” because he struggled to respond to a simple question, but he was ultimately able to hold a conversation. He described Mr Floyd as “friendly and approachable… living his life”.

The court was shown surveillance video, showing Mr Floyd laughing, talking to people, and walking around.

Mr Martin told the jury he sold Mr Floyd a packet of cigarettes, and received a counterfeit note as payment. He said he considered letting the shop deduct it from his wages instead of confronting Mr Floyd, but then decided to tell his manager. Another employee went on to call the police.

Mr Martin said he felt “disbelief and guilt” because “if I’d have just not taken the bill, this could have been avoided”.

What else has happened in the trial so far?

In opening statements on Monday, Prosecutor Jerry Blackwell told the jury that Mr Chauvin had “betrayed his badge” by kneeling on Mr Floyd’s neck, and using “excessive and unreasonable force” to detain him.

Meanwhile, Mr Chauvin’s lawyer Eric Nelson said the case was about the evidence, not about a “political or social cause”. He said Mr Floyd had ingested drugs at the time of his arrest “in an effort to conceal them from the police”, and suggested this contributed to his death.

Four young witnesses took to the stand on Tuesday. Darnella – the teenager whose film of Mr Floyd’s death sparked global protests – said she “stays up apologising” to him for “not doing more”.

She told the court she started filming on her phone because she “saw a man terrified, begging for his life”.

“It wasn’t right – he was in pain,” she said.

One witness, Donald Williams II, who is trained in mixed martial arts, was questioned for more than an hour by the prosecution and defence on Monday and again on Tuesday. He told the court Mr Chauvin had used a dangerous technique called a “blood choke” and was moving his knee back and forth to increase the pressure on Mr Floyd’s back and neck.

He rejected defence suggestions that he and other bystanders’ interactions with police had been threatening to the officers there.

Genevieve Hansen, a Minneapolis firefighter and emergency medical technician who was off duty at the time of the arrest, said she was “desperate to help” Mr Floyd but officers would not let her.

Mr Chauvin has been silent but remained engaged during the proceedings, taking almost constant notes on a yellow legal pad while listening to the evidence.

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Why is this case so important?

The video footage of Derek Chauvin kneeling on George Floyd’s neck last May was watched around the world.

To many, Mr Floyd’s death in police custody became a symbol of police brutality – particularly against people of colour – and it sparked mass demonstrations for racial justice.

But despite the global outcry this is not an open and shut case. In the US, police are rarely convicted for deaths that occur while they are on duty, if they are charged at all.

The verdict in this case will be widely seen as an indication of how the US legal system treats deaths that occur while in police custody.