APA style of citing legal materials is based on
The Bluebook

[The Bluebook: A Uniform System of Citation (16th ed.). (1996). Cambridge, MA: Harvard Law Review Association.]

U.S. Supreme Court Decisions

Name v. Name. Vol. number U.S. Page number. (Year).

Decisions of Lower Federal Courts

Name v. Name, Volume number Reporter abbreviation Page number (Court Name).

Federal Statutes

Name of Act § Section number, Volume number U.S.C. § Section number (Year).
Name of Act, Pub. L. No. Number , § Section number, Volume number Stat. Page number.

State and U.S. Constitutions

Co. Const. pt. 1, art. XV.
U.S. Const., amend. XIV, § 1.

Congressional and Federal Legislative Materials

Hearing - Title of Hearing, Number of Congress Cong. Page number (Year) (testimony of Name of witness).

Bill -  Title, Bill or Resolution Number, Number of Congress Cong., Number of Session Sess. (Year).

Reports and Documents - Series abbreviation No. Number, Number of Congress Cong., Number of session Sess. Page number (Year).

Abbreviations
Senate Report.: S. Rep.
Senate Document: S. Doc.
House Report: H.R. Rep.
House Document: H.R. Doc.