There needs to be general acceptance of the particular scientific methodology that experts use to give their testimony. Another legal rule that is considered is the Federal Rules of Evidence Rule 702 which provides the criteria that experts must meet to testify in court. These well-established rules state that an expert testimony must be (1) related to knowledge beyond what the layperson knows or clears any common misconceptions, (2) consist of an expert that qualifies by specialized knowledge, training or education on the subject matter, and (3) based on the reliable scientific information.
However, it is clearly inadmissible in court when experts use a defendant’s background and personality traits to prove the context. The experts cannot use character evidence as a means to prove that the defendant committed the crime in questioned (FRE Rule 404 (b)). Evidence is also inadmissible when the prejudicial value outweighs the probative value (FRE Rule 403). This