Gang Reduction, Investment, and Prevention Act

Gang Reduction, Investment, and Prevention Act - Authorizes the Attorney General to: (1) designate and provide assistance to high-intensity gang activity areas in specified states and localities; (2) make grants to develop community-based programs for gang members and high-risk youth; (3) expand the Project Safe Neighborhoods program; (4) expand the Safe Streets Program of the Federal Bureau of Investigation (FBI) to support criminal street gang enforcement teams; and (5) make grants for demonstration projects to carry out innovative approaches to combat gang activity.

Directs the Attorney General to establish a National Gang Activity Database to provide information to law enforcement agencies about criminal street gangs.

Directs the Office of Justice Programs of the Department of Justice (DOJ) to establish a National Gang Research, Evaluation, and Policy Institute to implement programs to combat gang violence, including conducting a national conference to teach and promote gang violence prevention, intervention, and reentry strategies and establishing one or more gang intervention academies to promote effective gang intervention and policing.

Amends the Violent Crime Control and Law Enforcement Act of 1994 to authorize grants to assist prosecutors and law enforcement officers in investigating and prosecuting gang members and violent offenders.

Amends the Juvenile Justice and Delinquency Prevention Act of 1974 to expand the number of sites receiving juvenile delinquency reduction grants from 4 to 12. Extends funding for the Mentoring Initiative for System Involved Youth Program through FY2013.

Establishes in the U.S. Marshals Service a Short-Term State Witness Protection Section to provide protection for witnesses in state and local trials involving homicide or other major violent crimes. Authorizes the Attorney General to make grants to prosecutor's offices to identify witnesses in need of protection.