Just because the partner isnt talking publicly does not mean he is covering for this a$$hat. It is more than possible that the partner is talking to the investigators and will be a witness for the prosecution. There are several reasons he might not be talking to the media that have nothing to do with a cover up.
According to the Sydney Morning Herald, the DA says the partner gave them #^#^#$. BS in other words. Here is the quote: “So I can’t talk to her because she’s gone, and the other cop just gave us some [expletive], OK. So guess what. I gotta figure out angles of the shot, gun residues, reckless use of force experts.” https://www.smh.com.au/world/north-america/police-officer-charged-with-murder-over-justine-damond-shooting-20180321-p4z5d2.html
If he talks to the media it makes it all the harder to prosecute the guy.
Jury selection is going to be more difficult and he might let something slip that could be used very effectively against the murderer.
I wouldn't talk to the media either.
Ever.
Maybe he can't hear the questions because his hearing still hasn't returned, after having a pistol fired next to his head inside a car.