Numerous academic studies and investigative commissions have documented police lying under oath in search and seizure cases.
“Dropsy”
Mapp v. Ohio—the 1961 case in which the U.S. Supreme Court ruled that illegally obtained evidence can't be used in state as well as federal trials—caused an epidemic of police perjury. Before Mapp, a police officer would testify that he or she had stopped a defendant for no reason, conducted a search, and found drugs. Although the search was illegal, the evidence was admissible because the Court had not yet decided Mapp. The police officer had no reason not to testify truthfully because it made no difference in the outcome of the case. After Mapp, if police told the truth about such illegal searches, the result was that the courts suppressed the evidence obtained from them. Police soon learned that if a suspect first drops narcotics on the ground and then an officer arrests him or her, the search is legal and the evidence is admissible. The “dropsy” problem has spread throughout the United States. Faced with the choice of believing either a police officer or a drug dealer, judges in courtrooms across the county tend to accept the police officer's false testimony.
The Mollen Commission
The Mollen Commission—set up to look into reports of police corruption in the New York Police Department—described the pervasive nature of police perjury in its 1994 report. It stated that the practice of police falsification in connection with arrests is so common in certain precincts that police themselves call it “testilying.” According to the commission, officers tell a litany of manufactured tales. When officers unlawfully stop and search a vehicle because they believe it contains drugs or guns, they sometimes falsely claim in police reports and under oath that the car ran a red light (or committed some other traffic violation) and that they subsequently saw contraband in the car in plain view. To conceal an unlawful search of an individual who officers believe is carrying drugs or a gun, officers occasionally falsely assert that they saw a bulge in the person's pocket or saw drugs and money changing hands.
The blue wall of silence
It is extremely difficult to prove perjury cases against police because of the informal rule among police officers that forbids one police officer to testify against another. The Christopher Commission, which investigated the police beating of Rodney King in Los Angeles, found this tendency of police to back up fellow officers to be an obstacle in its investigation.
Solutions for “testilying”
William Bratton, former police commissioner of New York, announced in 1995 a program under which all New York City police officers would be trained to give accurate testimony in court. Alongside programs to teach police how to testify truthfully, there are calls for the abolition of the exclusionary rule. Police typically give perjured testimony to cover up illegal searches and seizures. The exclusionary rule gives police an incentive to lie in order to avoid letting a suspect they think is guilty go free. Civil libertarians counter with the argument that it is unwise to get rid of the exclusionary rule until the government can put in place another mechanism to assure that the police comply with the Fourth Amendment.