More on this topic. The Trans Journalists Association put out this statement:
https://newsletter.transjournalists.org/tja-statement-on-the-covenant-school-shooting/
Which partially says:
The TJA's guidance is to not assume someone is cisgender or transgender based on their appearance, gender presentation, or pronouns. Police reports, public documents, or statements from family members can likewise incorrectly identify a person's gender. Even social media profiles can be misleading, outdated or incomplete.
So, going by this guidance, we can't make any determination about the shooter's gender. In that case, I am not sure if we can use any pronouns with regard to the person.
Note, I have never heard of the Trans Journalists Association until just now and have no idea if it is credible and/or representative. But I learned about this statement via a journalist that I trust and who has credibility with the trans community.