In 1997, Stephen Cowans was convicted of shooting a police officer and was locked up in jail after two fingerprint experst proved that the fingerprints, which were found in the crime scene, matched the man's. However, it turned out later the fingerprints were made by someone else. This is shown that fingerprint evidence is not always completely reliable. Fingerprint examiners, for example, can make errors and some experts are not even required to pass certification exams. Thus, in these case, the so-called experts are imcompetent and the fingerprints sometimes can be the unstable evidence for proof of guilt.