The main problem with a potential coworker doing this is that if they were absent that day or ducked out early, you'd think other employees and/or investigators would've noticed it.
At this point it looks like there are at least three main suspects.
1. Number one appears to be the former science teacher. I'm not going to mention his name, but the guy was a middle school science teacher at another school 20-30 minutes away from Bay Village when Amy disappeared. He was never married and often worked 16-hour days at the middle school. Apparently, he had snakes, fish and rodents in his classroom and would sometimes donate extra mice to the nature center in Bay Village. This individual also had a small room with a cot in it next to the classroom. Students would sometimes stay after class (and show up on weekends) to help clean reptile and fish tanks for 'extra credit'. He not only looks exactly like the composite sketch, but he also drove a gold Pontiac Grand Prix. Gold fibers were found on Amy's clothing after she was recovered in Ashland County. This individual also grew up on a farm in New London a couple miles from where Amy was found. He also had lots of relatives that lived in and around the New London area including his mother. I'm not going to type all the other interesting details about this guy because you can read all about them online. Suspect number one is currently 79 years old living in Key West, Florida.
2. Number two appears to be a guy (mentioned a few posts above) I'll call 'the Ex' because the former girlfriend of this guy identified him as a suspect in January 2019. Why she waited this long I have no idea but maybe she was afraid of him I don't know. When Amy disappeared, this guy lived with the girlfriend less than a mile and a half from the Bay Village shopping center. In a sworn affidavit, the former girlfriend said the man did not come home the night Amy disappeared. This was highly unusual according to her. She also claims he called her around 10PM that night and asked her if she was aware of the news coverage of Amy's disappearance. She also claimed she travelled with the man to Ashland County "on one or more trips". According to investigators, the man's appearance in 1989 was consistent with two major suspect composites obtained via witness interviews. This man also drove a gold Oldsmobile with a tan interior in 1989. Now even if you discount the former girlfriend, this next part is more than a little interesting. According to court records, an FBI agent noted a gold Oldsmobile registered to the man drove through an intersection near where Amy's body was dumped on the day she was discovered. A Bay Village detective wrote, “investigation has not been able to show any reason(s) why [the man] should have been near Amy Mihaljevic’s body recovery site on 2/8/1990.” According to police, the woman also told investigators that the man said his niece and brother’s family knew Amy. Police also said the man’s niece was the same age and in the same grade as Amy. Suspect is currently 66 years old and homeless/living in his car.
3. Number three was apparently a middle school math teacher at one point and the brother of Amy's riding instructor. I couldn't find any other info about this individual so that's all I really know about him.