I don't think they have a photo or video footage. I think they only have a report from someone saying a car of the description was near the crime scene.
I also think LE has a valid reason for asking for help finding this vehicle although the ask may seem too vague in the opiníon of non-LE.
You ask is it fair to report to LE or for LE to stop anyone driving or in possession of such a vehicle. Because of the seriousness of the crime, I think they do have cause. This is not a hit & run. It is mass murder. JMO!
Cops set up drunk checkpoints on some holidays. As long as civil rights are observed, such stops have been declared legal, I believe.
I am not in favor of guilty until proven innocent approaches by LE since it violates Constitutional rights but there are exceptions that are valid IMO. Overreach tends to be litigated so that protects rights at least to a degree.
MHOO