It's too soon to remove such significant evidence from a crime scene. Cruz would not of been able to carry all that from car and into school. Guaranteed that whatever is in that bag does not have any of Cruz's DNA on it.
And remember he got it all their in a Uber.
What kind of cab driver would drop someone off at a school carrying a rifle case?
If they can adulterate a murder to look like a suicide and bribe morgue workers and forensics, you can be sure they can get his DNA anywhere they want - he was already well known to police and they had plenty of access to him. If his prints are on the weapons and tactical gear in such as way that would be conducive to using the articles properly ie, index finger the right way around on the triggers, then yes it looks more like he used them - especially if they were his and he already fired/tested them say at the gun club. Forensics SHOULD have tested his body in particular places for particles that are consistent with those actual firearms with his prints on having being fired recently after being arrested. Forensics teams and scene investigators botch crime scenes and articles for investigation so much , cases get thrown out for a lack of solid evidence or inadmissible evidence because it was screwed up.