Bloodstains provide clues as to how a crime had been committed. When a speck of blood falls on a surface, it leaves a shape and stain. This is called bloodstain evidence. Each individual carries DNA that is unique to him or her, except for identical twins. With the help of bloodstains and saliva, as well as fingernails, an investigator can recover enough evidence to confirm whether a defendant is guilty or innocent of a crime. This book includes sidebars that further expand on the topic, as well as a further reading list and career information for readers interested in this intriguing STEM field.