Downloading movies illegally is a violation of both state laws and federal copyright laws. It is illegal to download them to a computer or other device or to offer such movies for sale. It is a felony under the U.S. Code to download and possess movies in violation of copyright law, and in some states it is also classified as a felony violation of state law. The federal crime is punishable by up to 5 years in prison, a $250,000 fine or both.
Determine the scale of the person's illegal downloading activities. If the person is downloading only a handful of movies for personal use, federal authorities will most likely not initiate an investigation. In that case, the activity will have to be investigated under state law.
Collect whatever information you can about how the person is accessing the illegal movies and where he is storing them. The particular website the person is accessing and which computer or other device she uses is particularly useful information. If he is reproducing the movies and selling them, information about where and to whom the sales are made is important.
Contact the appropriate law enforcement agency and report the crime. Provide them with all the information you have. They may request that you provide a statement regarding your knowledge of the illegal downloading.
Cooperate with the police if you want the person to be prosecuted for illegally downloading movies. If the offender's activity is confined to her residence or personal electronic devices, prosecution could be difficult otherwise because most local agencies lack the resources and expertise to build an adequate case without witness testimony.