The Minneapolis police chief, Medaria Arradondo, told the Derek Chauvin murder trial on Monday that he “vehemently disagrees” that there was any justification for the former police officer to keep his knee on George Floyd’s neck for more than nine minutes. Arradondo said on the sixth day of the trial that Chauvin’s treatment of the 46-year-old Black man breached regulations and showed a disregard “for the sanctity of life”. “Once Mr Floyd had stopped resisting, and certainly once he was in distress and trying to verbalise that, that should have stopped,” he said. The police chief said that while it might have been reasonable to use a certain level of force “to get him under control in the first few seconds”, Chauvin’s subsequent actions did not meet the standard of “objectively reasonable force”. “To continue to apply that level of force to a person proned-out, handcuffed behind their back, that in no way, shape or form is anything that is by policy,” he said. Arradondo said that far from being aggressive, Floyd appeared to be completely passive. “As a matter of fact, as I saw that video I didn’t even know if Mr Floyd was alive at that time,” he said. It is highly unusual for a police chief to give evidence against one of his own officers. Arradondo, his city’s first Black police chief, fired Chauvin shortly after Floyd’s death. Chauvin, 45, has denied charges of second- and third-degree murder, and manslaughter. He faces up to 40 years in prison if convicted of the most serious charge. Three other officers face charges. Floyd’s death last year reinvigorated the Black Lives Matter movement and prompted mass protests for racial justice across the US and other parts of the world. The prosecutor spent the day on Monday building a case that Chauvin failed to follow his training to consider whether Floyd’s resisting arrest was “a deliberate attempt to resist or an inability to comply” because of issues such as medical conditions, mental impairment or the influence of drugs. On Thursday, Floyd’s girlfriend testified that he was addicted to opioids and another witness said that he appeared to be high shortly before his arrest. Arradondo agreed that a person under the influence of drugs might be more vulnerable than dangerous. The police chief said that Chauvin should have considered a number of factors in how he dealt with Floyd. “Is the person a threat to the officer and others? What is the severity of the crime? Are you re-evaluating and assessing the individual’s medical condition?” said Arradondo. Considering all those issue, the police chief added: “I vehemently disagree that that was an appropriate use of force”. He said that Chauvin also appeared not to have been following his training to de-escalate a confrontation. “You want to always have deescalation layered into those actions of using force,” said Arradondo. Chauvin’s lawyer, Eric Nelson, put it to Arradondo that the use of force, such as an officer pointing a gun, could be a de-escalation tactic in certain circumstances if it prevents greater violence. The police chief was hesitant but said it could sometimes be the case. The police chief questioned the need to detain Floyd at all, saying that it would not be normal to arrest a person for passing a counterfeit bill because “it’s not a violent felony”. The prosecutor also drew Arradondo’s attention to the failure of Chauvin and the officers with him to render medical assistance to Floyd when he stopped breathing. The police chief said that all officers are trained in first aid and “absolutely have a duty” to render it to a person having a medical crisis such as Floyd when he said he could not breathe and then passed out. Earlier on Monday, the emergency room doctor who tried to save Floyd’s life told the trial he most likely died of asphyxiation. Dr Bradford Wankhede Langenfeld said he saw no evidence Floyd was killed by a heart attack or a drug overdose as Chauvin’s defence has claimed in attempting to deny that the death resulted from the officer keeping his knee on the detained man’s neck for more than nine minutes. Langenfeld, who declared Floyd dead, told the court there was not a heartbeat “sufficient to sustain life” and that he believed cardiac arrest was brought on by “lack of oxygen”. He was asked by the prosecutor if there was another term for that. “Asphyxia,” said Langenfeld. The doctor said he thought a heart attack was unlikely because when he cut open Floyd’s chest he saw no evidence of that. He also said the paramedics who brought him to the hospital said Floyd showed no behaviour typical of the condition. “There was no report that the patient complained of chest pain or was clutching his chest,” he said. The state medical examiner found that Floyd’s death was caused by “cardiopulmonary arrest”, which the prosecution says is a broad enough term that can be applied to any death because it means only that a person’s heart and lungs have stopped. The defence claims the finding means Floyd died of a heart attack. Langenfeld told the court a delay in treating Floyd, particularly giving him CPR, may have reduced his chance of survival. Ambulance paramedics reported that the police made no effort to give Floyd medical assistance even though he had passed out and was unresponsive by the time they arrived on the scene. The trial continues.