Jody Stiger, a Los Angeles Police Department sergeant, testified Wednesday that former Minneapolis police officer Derek Chauvin used "deadly" force on George Floyd and kept his knee on Floyd's neck for more than nine minutes.

Why it matters: Stiger, a prosecution witness, said the initial force Chauvin used on Floyd was appropriate, but he should have let up when Floyd stopped resisting.

• Chauvin faces murder and manslaughter charges.

What they're saying: “As the time went on in the video, clearly you could see Mr. Floyd’s medical — his health was deteriorating. His breath was getting lower. His tone of voice was getting lower. His movements were starting to cease," Stiger testified.

• "So at that point, as an officer on scene, you have a responsibility to realize that, ‘OK, something is not right. Something has changed drastically from what was occurring earlier.' So, therefore you have a responsibility to take some type of action.”

Chauvin's defense questioned Stiger about uses of force that are “lawful but awful," and Stiger agreed that “you can have a situation where, by law it looks horrible to the common eye, but based on the state law, it’s lawful.”

• But Stiger told prosecutors that the "lawful" force must be "objectively reasonable."

The big picture: Johnny Mercil, a use-of-force instructor at the Minneapolis Police Department, testified Tuesday that officers are trained to use the "least amount of force necessary" to subdue a suspect, and that a knee on the neck would not be authorized against a suspect who is "under control and handcuffed."

Go deeper: Minneapolis police chief: Chauvin "absolutely" violated department policies