If you have a big amount of BTC, is there a way to transfer or withdraw the amount without getting the bank or the authority suspicious of you?
Yes, there are ways to exchange your bitcoins to your local currency without raising any alarm. However, if you want to cashout all your bitcoin at once, alarms will be raised by the bank itself. Banks are very strict with the AML (Anti money laundering) norms and any unrelated transactions are reported to the enforcement agencies.
So the best thing you can do is transfer small amount. Use localbitcoins website to exchange your bitcoins to your bank account. Instead of exchanging the whole amount at once, use small fractions on weekly basis or monthly basis. A huge amount of money will draw immediate attention. But small transfers will go unnoticed. Play smart!