"For example for police force, they cannot play too tough due to law restriction, then those really bad guys basically don't give a fuck, so it may not work. "
Isn't the point of Scharffs Method that you do not have to be tough? You can be friendly.
Neutral ... in general you are having a conversation - you are not pushing - and therefore the tough guys do not feel pushed and do not block and reveal information without realising it.
If you read news stories about the mueller investigation you can catch glimpses of this as people who have been interviewed tell reporters over and over again that it’s close to wrapping up.
I’m sure everytime everyone is interviewed the agent tells them they’re just wrapping up a few loose ends and they think the whole thing is a big misunderstanding.
Or that the people who are being interviewed individually have no leads so from their vantage point the investigation perpetually seems to be wrapping up (because there seem to never be any new leads) except every now and then they find someone they can nail for the typical process crimes wall street/Washington elite engage in.
Then there's the whole political angle. One side wants this to seem like the investigation is chasing nothing and should have ended a long time ago. The other side wants it to seem like a damning report will come out tomorrow.
Isn't the point of Scharffs Method that you do not have to be tough? You can be friendly. Neutral ... in general you are having a conversation - you are not pushing - and therefore the tough guys do not feel pushed and do not block and reveal information without realising it.