They were never sure.
It was in the 80’s and there were apparently several serial killers traveling the roads picking up hitchhikers.
Each serial killer had a similar MO so they didn’t know if there was some kind of connection between the killers or if there were copycat killers.
The number of similar killings was in the hundreds IIRC, and they were taking place all over the country some around the same time.
They tried to make the claim Lucas was responsible for something like 600 killings, but that was reduced way down.
GWB commuted Lucas's death sentence. I wonder if his confessions were just an elaborate attempt at suicide via the correctional system.