Not so pro Tip -- if you're being investigated and they're ballsy enough to finally send a guy to sit right outside your house and take notes on everything they see all day long... You can just walk up to them and ask wtf they're doing... When they say working, tell them to GTFO, they're loitering and parked in the road illegally.

If the target knows they're being investigated for a few months and knows that if there's no probable cause to take further action within a certain time frame, they might just go ahead and not change routine and give away nothing and wait it out.

This has only happened to me twice.