Unlike "suspect" and "material witness," "person of interest" has no legal definition, but generally refers to someone law enforcement authorities would like to speak with or investigate further in connection with a crime. It may be used, rather than calling the person a suspect, when they don't want their prime suspect to know they're watching him closely. Critics complain that the term has become a method for law enforcement officers to draw attention to individuals without formally accusing them.
There is concern among critics that innocent people will be tainted by being labeled a person of interest.