I've not kept up closely with this trial but I believe these three didn't actually beat Nichols, but rather didn't stop the two who were actually beating him. The two who beat / kicked him to death have already pled guilty to federal and state charges.
I read an attorney's description of the charges and he said the bodycam footage proved them not guilty based on the jury's instructions, some of which were:
Not defending anyone here, just posting what I've been reading.
To be 100% clear, Tyre Nichols was murdered and didn't deserve the way he was treated.