When does an agency report its investigations to the FBI?

Question

This is pertaining investigation reports not convictions.
If a police dept is conducting an investigation, lets say an internet sting on possible online predators, will it report all its findings to the FBI or only those that are being investigated that cross state lines.
another example would be investigations on a possible drug dealer, do they only report the suspect to the FBI when he/she crosses state lines?

Answer 1

This has a lot of "ifs" in there.

From what I understand, there is always a "lead agency". It is usually negotiated from high on up. All other agencies then report to the lead agency. Nowadays, it'll probably be DHS.

Local police cybercrime unit can do their own investigation, and they can request an FBI liaison as FBI has a cybercrime task force as well, but they don't really report to each other except data sharing, as all such data are pooled at the National Crime Database. If the project is expanded, a new special task force can be formed and new lead agency assigned, then it may no longer be under local purview.

FBI usually don't touch drug cases. They leave that to the DEA, though nowadays they are supposed to work for DHS and "we're all on the same team" and all that. Again, depends on decisions from higher-up. Unless this dealer is pretty darn big, FBI/DEA usually leave that to the locals.