Comment by kube-system

Reasonable suspicion is required for a terry stop but that does not apply at a border crossing. Everyone can be stopped and questioned and searched at a border crossing.

An ”investigation” is just a fancy word that broadly describes the type of information collection that law enforcement does. Yes, it is typically about things they think are crimes. Because that’s their job. But there’s not some legal hurdle they have to pass here, the word describes their work.