I know I'm not the first to suggest this an investigative tactic, but why not use Delphi 2016/2017 census demographics cross referenced with Indiana drivers liscences to narrow down the suspect pool? It is really just a process of elimination and should be simple for investigators who have access to records. Here is a loosely researched example:
Online research suggests there were 2882 residents in Delphi in 2017. IF BG is in fact a local, than he should be one of those people.
Slightly over 50% of that population is female, and I think we all agree BG is male, so that cuts the pool to 1470 suspects.
Although the composite sketch of BG appears to be a young person, I doubt he is a child. Therefore I think you could safely eliminate anyone who was under the age of 16 at the time of the murders. I'm not sure of the stat on this one, but there are approximately 1477 students registered in the Delphi school district, and assuming that half of those are female (738), you can subtract those out of the pool, leaving only 739 people to investigate (obviously infants and toddlers could also be eliminated, further reducing this number).
Once again based on the youthful appearance of BG in the sketch I think you can safely eliminate all of the senior citizens in Delphi. I'm not sure what this number would be, but since Delphi's mean age is older than the US average, I'm assuming there are some seniors in town. For the sake of a guess-timate, lets say you could eliminate 100 older men. Suspect pool is down to 639.
BG appears to be caucasian in the video and sketch. Only about 13% of Delphi's population is not 'white' (but that is still about 374 people). The next step would be to eliminate the males aged 16-60 who do not have light skin. I'm just guessing at a number, but say you could cross off another 100 from the list, leaving 539.
There would be a handful of people who were incarcerated, hospitalized, or in care homes at the time of the murder. Cross these people off and you might be down to about 500 suspects.
I doubt that BG has a severe disability, so anyone who is blind, deaf, developmentally delayed, or requires a wheelchair for transportation can also be eliminated.
BG speaks English, so anyone who cannot can also be eliminated.
From this pool of fewer than 500 residents, LE should be able to eliminate those who were without question out of town on Feb. 13, 2017 and/or accounted for at work during the hours the abduction/murders took place. Cross-reference the names left on the list with their photo ID to see who most closely resembles the individual in the sketch. Assign officers to investiage the 10-20 people from this list who most closely fit the look to see if any also fit the profile or are already on their radar.