The grocery store cashier responsible for flagging a counterfeit $20 bill prior to George Floyd's arrest and death has spoken out about his "disbelief and guilt".

Nineteen-year-old Christopher Martin spoke in court on Wednesday about the events leading up to Floyd's death, during the third day of Derek Chauvin's trial.

Chauvin is currently facing charges of second-degree murder - with a sentence of up to 40 years in prison - third-degree murder, and second-degree manslaughter, CBS News reports. He has pleaded not guilty.

As reported by The Independent, Martin was working as a cashier at Cup Foods on May 25 last year, when Floyd visited the store.

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Speaking with prosecutor Matthew Frank, Martin revealed to the courtroom that he spoke with Floyd about sports - with the late 46-year-old telling the teenager that he played football.

"When I asked him if he played baseball, he went on to respond to that, but kind of took him a little long to get to what he wanted to say, so it would appear that he was high," Martin said.

Jurors were shown surveillance footage of Floyd inside the store during Martin's testimony.

After Floyd purchased a packet of cigarettes with a counterfeit $20 bill, Martin suspected it was a fake after noticing a blue pigment on the note - similar to how a $100 bill would, he explained.

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The surveillance footage shows Martin Martin, holding up the note to inspect it. Martin says that he did accept the bill, saying: "I thought George didn’t really know it was a fake bill so I was doing him a favour."

Worried that his wages would be docked the amount for the counterfeit note, Martin then said: "I second-guessed myself and kept examining it and eventually called my manager."

After alerting his manager, the clerk - who had only worked at the store for four months - was ordered to call Floyd back into the store.

Walking outside to speak with Floyd, Martin said of their interaction: "[Floyd] just seemed like he didn’t want this to happen.

"He was kind of like, 'Ah, why is this happening?'"

Per the New York Times, Floyd and the passenger in his car refused to re-enter the store, and despite Martin claiming to pay for the cigarettes himself, his manager requested that another staff member call the police.

George Floyd was held to the ground by officers for approximately nine minutes, with footage recorded by bystanders showing Chauvin holding his knee on Floyd's neck. Floyd can repeatedly be heard telling the officers in the footage: "I can't breathe."

Floyd died shortly after.

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"If I would’ve just not taken the bill, this could’ve been avoided," Martin said in his testimony.

When asked by prosecutors what he was thinking watching Floyd's arrest unfold outside the store, Martin said he felt "disbelief and guilt".

The Metro reports that Floyd's autopsy showed evidence that he had consumed fentanyl and methamphetamine prior to his death, but prosecutors have argued that the amount would not have been fatal to him following years of addiction.

Featured image credit: MediaPunch / Alamy

Cashier who flagged counterfeit $20 bill reveals his 'disbelief and guilt' over George Floyd's death