For cops who kill, special Supreme Court protection

So Aldaba took the only other route open to people in her situation: She sued. Her lawsuit in federal district court in Muskogee, Oklahoma, alleged that the three officers used excessive force, violating her son’s civil rights under the Fourth Amendment to the U.S. Constitution, which protects against unreasonable search and seizure.

But almost immediately, her case hit a formidable obstacle: a little-known legal doctrine called qualified immunity. This 50-year-old creation of the U.S. Supreme Court is meant to protect government employees from frivolous litigation. In recent years, however, it...