How we can trust forensic accountant and to what extent thier efforts will be successful?

I found this informative article from WIPFLi CPAs which advises you what to look for when choosing a forensic accountant: http://www.wipfli.com/resources/images/16623.pdf

Forensic accounting itself is extremely effective in uncovering defalcations. Just be certain of their experience in the area when you engage them. They are by nature "diggers" and not only will take the time to trace the tedious cash trails; they will have a grasp of reasonableness in industry transactions and tend to look into areas you may not think of.

I can not tell you with certainty the level of success, but I can almost guarantee that they will be able to find the things you are not aware of. Good luck with your audit.

I am curious, have you defined success for the company from this project? What is the goal of hiring a forensic accountant? Depending on this you may or may not need a "forensic" accountant. If you are involved in a large court case, then you may want to make sure the accountant meets the highest possible criteria.

For example, a client hired me to review the balance sheet of a subsidiary. What I found was a failed accounting software implementation. As part of the re-implementation, we had to go in and re-construct certain accounts at the time of implementation and then we had to determine the company's financial position at the end of the prior year, then walk the accounting current, closing each period . . . All requiring "forensic" accounting skills, but none of the team was a "forensic" accountant.

Hope this helps.

Best regards, Kim