DNA fingerprinting depends on one very important factor- the fact that every person, animal or otherwise all have different DNA fingerprints. If more than one person had the same DNA fingerprint, then it would throw the entire system out of whack.
You would not be able to convict anyone of a crime, to be able to even tell that the DNA belongs to multiple individuals, and it would make it very unreliable. Thankfully this is not the case and DNA fingerprinting is incredibly accurate and precise. In the same way that everyone has different fingerprints, everyone has a different DNA fingerprint or profile.