People keep going on about the knee on neck, you know it doesn't take much pressure on your neck at all to hinder your ability to breathe or even talk. GF was happily shouting at the top of his lungs for ages.
If DC did indeed have his knee on GFs neck, and was using all of his body weight, GFs larynx would have been severely compressed completely limiting his ability to talk/shout and likely breathe at all. I think any breathing difficulty he had was not as a result of the restraint and entirely to do with the covid/drugs in his system all of which are known/proven to cause serious respiratory complications. Neither of which the cops would have known about right away. They are also well aware of his prior history and would have made a judgement call about him being truthful or telling lies.