I watched him say it on TV. He said that in response to a reporter pressuring on why there have not yet been any charges, and he responded with saying “there is other evidence that does not support a criminal charge” in the tone that he will charge in due time, but does not want to be rushed to be sloppy. He did not come across as he was unlikely to charge the officers as you have interpreted it. You can watch a clip of him saying it here:
https://twitter.com/BNONews/status/1266136952874696709
I think he chose his words carefully. That’s a bizarre thing for a district attorney to say. If he said we are examining all of the evidence, I could understand that. I think he is quite clearly suggesting that this case isn’t as airtight as everybody thinks it is. But, again, I’m not reaching any firm conclusions. I do find it quite strange that the medical examiner was unable to determine a cause of death yet without the need for further testing.