LE have made various statements including confirming the sketches are of two different men, or the suspect might not look exactly like either sketch. JMO what that’s suggesting is they don’t want anyone to get too hung up on the likeness to a sketch - now three years old to boot.
It’s important to note that sketches are not photographs - a sketch is only as similar as the accuracy of a witness’s memory.
Another thing is very important to consider - the murders of Abby and Libby were not witnessed by anyone. Nobody saw anything that warranted reporting a situation to LE while the girls were only considered missing as no foul play was suspected in their disappearance...until their bodies were found.
So hypothetically to explain the two different sketches, I can see a scenario happening such as this - during the investigation, officers attempt to piece together who was where at any given time. One or more witnesses saw somebody, somewhere who LE decided given time/location, etc must have been an actual sighting of the suspect, so sketch #1 was created and released.
Then later, for whatever reason LE began to doubt it was the suspect connected to that particular sighting. Maybe they located the sighted person, determined the timeline didn’t fit, or began to doubt the witness’s credibility - they never told us the reason, only that the investigation was “changing directions”.
So they looked back into the files and determined another witness had made a different observation of somebody, somewhere and determined through their investigation this indeed was the suspect. So the different sketch was released, once again only as similar as the accuracy of the witness’s memory.
This is often how investigations go, POIs rise and fall to and from #1 suspect during the course of an active investigation. But usually LE doesn’t release a sketch adamantly declaring “this is our suspect” and then retract it later, then releasing a different sketch. I’m not sure the reason for that, hopefully we’ll learn the answer some day when the guilty perpetrator is arrested and tried.
JMO