42 U.S. Code § 10503 - Limitation on authority
Nothing in this chapter authorizes the use of Federal law enforcement personnel to investigate violations of criminal law other than violations with respect to which investigation is authorized by other provisions of law.
Nothing in this chapter shall be construed to authorize the Attorney General or the Federal law enforcement community to exercise any direction, supervision, or control over any police force or other criminal justice agency of an applicant for Federal law enforcement assistance.
No funds provided under this chapter may be used to supplant State or local funds that would otherwise be made available for such purposes.
Nothing in this chapter shall be construed to limit any authority to provide emergency assistance otherwise provided by law.