We have far "better" surveillance than we used to in the 80's there was the Tylenol poisonings of 82 and 86 - the 86 poisoning in Yonkers, NY killed some State Troopers family members that were close to my late father . The 82 poisonings/tamperings killed more folks in Chicago iirc.
afaik those cases were never solved.
Who ever is doing this may escalate, I'm sure the cops could catch him if they had a mind to
I've no knowledge of Forest City NC, but Googley maps shows about 20 gas stations in the immediate environs. Not sure how a small town cop shop could cover them all. Maybe with help from the sheriff's department, or nearby departments.
Obviously, they're looking at surveillance footage, but there may not be much available. Who knows?