Law breaking is an activity is not limited to just people who have all their faculties intact, but can quite often, include people who have some handicap. This at times, includes people who are hard of hearing or completely deaf, and depend on sign language for communication.
This is a language that the ordinary person or policeman will not understand, and then the need arises for a sign language interpreter for police interrogation work. As per the law, police are required to provide not only assistive listening devices like aids if needed, but also arrange for the services of a qualified interpreter of sign language, so that the deaf and hard of hearing person can be questioned.
The sign language interpreters are professionals who can help the police to question the hearing impaired person and interpret what is said in sign language to enable the police to record statements and take the necessary action that is needed in the case.