The supervisor of Derek Chauvin, who has been charged with killing African-American man George Floyd, on Thursday said there was no justification for the police officer to keep his knee on the 46-year-old man’s neck for nine minutes, reported The Guardian.

“When Mr Floyd was no longer offering up any resistance to the officers they could have ended their restraint,” said Sergeant David Pleoger. He was speaking at Floyd’s murder trial that began on Monday.

Video recording of the incident in May 2020 showed that Chauvin kept pressing his knee into Floyd’s neck even after he was gasping for air and pleading to the officer that he could not breathe. Two other police officers were also holding down Floyd, who died at the spot.

At the trial, Pleoger said police officers are trained to turn suspects on their side when they are restrained with handcuffs on the ground to prevent “positional asphyxia”, a condition that stops people from breathing adequately. “If they are left on chest or stomachs for too long, their breathing can be compromised,” he said.

Defence lawyer Eric Nelson attempted to play down the significance of the sergeant’s testimony, saying that Pleoger had “not reviewed the entirety of the evidence in this particular case”, according to BBC.

Two paramedic officers also told the court that Floyd had no pulse and did not appear to be breathing when they arrived at the scene. Paramedic Seth Bravindar said he had to ask Chauvin to get off Floyd so that they could access the patient.

Pleoger had arrived at the crime scene shortly after Floyd was taken away in an ambulance. He is expected to be called as a witness among other police officers, including Medaria Arradondo, the chief of Minneapolis police department. Arradondo had sacked Chauvin shortly after Floyd’s death.

Chauvin, 45, has denied charges of second and third-degree murder and manslaughter. He can be imprisoned for 40 years if convicted of the most serious charge in the case.

The defence has indicated that they plan to argue that Floyd died because of an overdose and poor health, and the use of force was reasonable. An autopsy had found opioid fentanyl and recreational drug methamphetamine in Floyd’s system, according to AP. However, the autopsy also revealed that Floyd died of asphyxiation due to neck and back compression.

Floyd’s partner recalls their struggles with addiction

At trial, Floyd’s partner Courteney Ross narrated to the jury how both of them met and their struggle with opioid addiction.

“Our story, it’s a classic story of how many people get addicted to opioids,” said 45-year-old Ross. “We both suffered from chronic pain. Mine was in my neck and his was in his back.”

Ross said they both had prescriptions for drugs, and when those ran out, they took the prescriptions of others or bought illegal drugs. She also told the jury that they tried “really hard” to get over their addiction many times.

”Addiction, in my opinion, is a lifelong struggle,” Ross said. “It’s not something that just kind of comes and goes. It’s something I’ll deal with forever.”

Ross’ testimony is an effort from the prosecutors to humanise Floyd and explain his drug use, according to AP. The testimony that Floyd struggled with opioid addiction could help prosecutors counter the argument that the African-American man died of drug use. Medical experts say that the level of fentanyl found in Floyd’s system could be fatal to many, but those using drugs regularly can develop a tolerance to it.

On Monday, when the trial began, Prosecutor Jerry Blackwell said that Chauvin had “betrayed his badge” and used excessive and unreasonable force. Several witnesses have taken the stand, including four children who were under the age of 18 at the time of Floyd’s arrest. They have spoken about their trauma at what they witnessed.

Shop employee Christopher Martin, who had alerted his manager that Floyd was using a fake bill to buy some cigarettes, also spoke about his “disbelief and guilt”. “If I’d have just not taken the bill, this could have been avoided,” he told the court.

Three other police officers – Thomas Lane, J Alexander Kueng and Tou Thao – are also charged with aiding and abetting the murder. They will go to trial later this year.

Floyd’s death had sparked widespread outrage and protests across cities in the US. There were some incidents of vandalism during the protests.