There exists software which is designed to confuse them and convincingly plant evidence; and while that software is imperfect, they are powerless against that.
I've been a digital forensics software developer for a decade. There's plenty of buggy software, yes, but I've never heard of software that deliberately plants evidence.
FLETC and other training classes instill in investigators the necessity of manually verifying and testing their results for their reports and/or court testimony.
Most cases involve child pornography. Most of the time its known child pornography (i.e., there's a known victim, there are likely other folks who have been convicted of possessing the images). Most of the time the suspect takes a plea bargain.
It's the rare case that involves figuring out who-did-what-when events on a computer based on trace artifacts. So, the good news is that they are not the norm; the bad news is that only the best examiners (on either prosecution or defense) can typically handle them.
There exists software which is designed to confuse them and convincingly plant evidence; and while that software is imperfect, they are powerless against that.