Murder expert witnesses practice in a variety of fields, including criminal law, forensic science, psychology, pathology, and ballistics. Some of the most common specialties among murder expert witnesses also include crime scene reconstruction, DNA analysis, mental health assessments, firearm examination, and toxicology. They have provided opinions on the effects of self-defense claims, evidence of premeditation, the psychological state of the defendant, cause of death determination, and gunshot residue analysis.