fink noun \ˈfiŋk\ : 1 informer. 2 one who betrays a trust.
When it suits his purpose, Brett Kimberlin will rat out someone else. This is from the decision of the Court of Appeals for the Eleventh Circuit in United States v. Sarmiento-Perez, [724 F.2d 898 (1984)]:
Appellant was also connected to the cocaine transaction by his admission to Brett Kimberlin, his cellmate. Kimberlin testified that appellant admitted his involvement in a drug transaction that appellant claimed to have gotten involved in as a favor for someone in his family. Kimberlin also testified that he vaguely remembered appellant telling him that the cocaine was in appellant’s car or in the car’s trunk.
Some people are willing to throw others under the bus.