I agree with that time frame. The area has probably been used as an off again, on again youth drinking spot. The perpetrator at 16- to early twenties would fit fight in.
The perpetrator at that age could also fall into two general categories
- Bad news types with a criminal record.
- Bad news types known to have deep criminal tendencies, but no convictions.
The first group can be identified using records searches. The second group might take interviewing retired teachers, police, probation officers, clergy and youth sport coaches. Maybe they remember a former resident youth known to be sexually aggressive, had deep seated criminal tendencies, cruel to animals, had continual fantasies about being a crime boss or serial killer etc.
The most promising candidates could then be followed up on.
Another source of local lore concerning bad news former residents might be class reunion coordinators. Maybe one noted a former bad news type drifting in to a reunion out of boredom and then re-visiting the area from time to time etc.
Likewise, if one wants to set the time of former residency at a slightly older age to be at youth drinking sites, maybe interview retired tavern owners, liquor store owners, and former dance club owners about bad news- but never convicted former residents.