Can we really stop malicious insiders?

In terms of malicious insiders committing fraud, can anything "really" be done?

There is a popular quote from the 2003 version of the film The Italian Job that comes to mind when I read this question. "I trust everyone. It's the devil inside them I don't trust." The threat from insiders, being fraudsters or otherwise, has always been there - certainly before security companies started talking about them. What has changed, and this is in direct response to the question, is that - yes, there are things that can be done, many in fact.

First, let's look at the advantages insiders have: Trust and access. Consider a college intern, Sam, working for a large financial organization. Sam's job requires him to enter payees into the corporate database, and to do this job he his granted access to the database. Sam eventually realizes that his access doesn't just allow him to create payees, but also pay those payees because of flawed access controls, lack of segregation of duties, poor policies, etc. Sam begins generating false payees associated with a PO Box he set up, and then has checks sent to that PO Box.