Blood Spatter Analysis
Blood spatter analysis was made most famous by the TV show Dexter which stars Michael C Hall as the eponymous anti hero Dexter who works as a blood spatter analyst for the Miami Police Department. Dexter is a vigilante serial killer who uses his position and forensic knowledge to get away with his crimes. Blood spatter analysis is a forensic science method which asserts that patterns left in blood after an attack can indicate information about the assailant.
Blood spatter analysis was one of the forensic methods reviewed by the FBI in 2016. When the FBI reviewed most forensic methods to assess their efficacy blood spatter analysis did not fare well in this closer examination. It was found that there was a huge variation in the interpretation of the results by different analysts. This indicates that these results are more ambiguous than previously thought.
The techniques can provide some insight into a crime scene and can certainly be used to determine the weapon used. The spray cast from a single gunshot is very different to the spray cast from a bludgeoning. The more detailed pieces of evidence as represented in Dexter, such as being able to determine the exact height of a perpetrator or how many people were involved, are open to interpretation to a greater extent and a different analyst may give a different interpretation. Though it can't be dismissed out of hand it should be treated with caution rather than as a hard fact.