rights of people

Q: I would like to ask if someone knows the truth and is hiding it from others in order to save the bad person or guilty one, what does the Qur'an and Hadith say about it?

Q: Whilst I was a non-Muslim I was involved in fraud, scams and conned a few people. Now that I have accepted Islam, I heard that Islam erases all previous sins. Will I be accountable for these sins as well since they relate to the rights of people?