Over the last two‑plus decades, the scientific validity of the principles that underpin identifying a firearm from recovered fired ammunition has been a core issue for the admissibility of expert evidence in criminal trials in the United States. The issues that dominated the determinative points, as they related to the scientific and technological analysis, centered around the following: the validity of uniqueness of firearms, subjective methodology, the potential rate of error, unknown statistical certainty and unsatisfactory proficiency tests. These issues have essentially become the legal requirement for admissibility of experts’ opinion on the linkage of firearms with fired ammunition, an important forensic opinion that connects the crime with the perpetrator through the weapon of offence. In Forensic Firearms in Criminal Trials: Legal, Investigative, and Scientific Aspects, internationally renowned forensic firearm expert Dr J. K. Sinha provides demonstrative explanations and helpful clarifications using simple illustrative examples from scientific casework and everyday life. The goals are to: Prove the scientific validity of the uniqueness of identifying features of firearms Identify the statistical threshold to qualify and determine a corresponding match Debunk the misconception of subjective methodology and the potential rate of error thereof in experts’ decision making and opinions Clarify the prevailing perception of similar, dissimilar and insufficient marks and consequential interpretation With certain non‑technical readers in mind as well, the book provides a basic understanding of the general make‑up of firearms and ammunition, the evidentiary values of commonly used firearms, fired empties, fired bullets and pellets, and scientific investigative leads that result from visual and physical evidence. Chapters cover related topics such as proficiency tests, identifying competent experts, admitted firing, and reliable and testable methodology. The book also reviews the admissibility of expert evidence in India and explains the proviso of admissibility of ballistic expert report in criminal trials. Throughout, the author emphasizes the need for requisite forensic knowledge by the investigator and aided by a competent expert for effective scientific investigation of gunfire crimes such as would aid in the proper presentation of scientific evidence at criminal trial for a successful outcome.