Could you expand a little on what you're referring to? Is this a specific vulnerability?

A powered down device rarely has that vulnerability.

A powered down device isn't exactly terribly useful.

You can't send a powered down phone a push notification for post-hoc analysis.

You would have had to know the target and push a vulnerability beforehand, which wouldn't have helped in this case.

So power it on? It will still boot with encryption. Isn't Android encryption is an extension of ext4 and only protects some data. It's not full disk / LUKS last I knew.