one of the more fun things I learned during criminal court in Texas is that the absence of forensic evidence cannot exonerate an individual. The prosecutor and the judge covered that despite not having any forensic evidence, the jury would still be expected to be able to convict the defendant. If you weren't OK with that you weren't eligible to serve on a jury.
They are trying to avoid a situation where you end up with one juror who watches a lot of CSI and insists that they need forensic evidence to convict, despite having a dozen eye-witnesses. If a juror cannot imagine a circumstance where the evidence could be beyond a reasonable doubt based on non-forensic evidence, then they aren't suitable to be a juror.
For example, if you're sitting in your living room with a bunch of other people, many of whom know each other, and two people start fighting, you are all witnessing a crime and you can also all identify the two people fighting. It would be ridiculous to require DNA evidence in that situation.
Was your prior assumption that forensic evidence must exist in every case—and that if it doesn’t, then there’s no way to convince a jury of someone’s guilt?
As in, as long as I clean up really well afterward, I can pretty much do what I want?
I think you're missing the slippery slope that this goes down. The criminal charges were way too low, given the alleged actions. The state admitted it had absolutely no forensic evidence. The judge was perfectly fine with this and selecting a jury that was OK convicting in this circumstance. This pretty quickly pretty us down a path of "you're guilty of at least one crime since you've been indicted, maybe a more serious one if we have some evidence".
Five (or fifty-five) people giving unambiguous eyewitness testimony that clearly identified the defendant and the crime he committed, with them all keeping their stories consistent under hostile cross-examination has exactly zero forensic evidence... but if you, as a juror, found all of that persuasive, it sounds like it should be enough to convict.