Question: The Commission to Investigate Alleged Police Corruption (known informally as the Knapp Commission) became informed of Frank Serpico's police corruption by him doing what?

Context paragraphs:
The Seven Five: The Seven Five, also known as Precinct Seven Five, is a 2014 documentary directed by Tiller Russell, and produced by Eli Holzman, Aaron Saidman, and Sheldon Yellen.  The film looks at police corruption in the 75th precinct of the New York Police Department during the 1980s.  The documentary focuses around Michael Dowd, a former police officer of 10 years, who was arrested in 1992, leading to one of the largest police corruption scandals in New York City history.  The documentary uses footage from the Mollen Commission investigation in 1992 and also provides in-depth commentary from Dowd, Ken Eurell, and Adam Diaz, among others.  The documentary premiered at DOC NYC November 14, 2014.  Sony Pictures recently purchased the rights of "The Seven Five" documentary in an auction.

Police corruption: Police corruption is a form of police misconduct in which law enforcement officers end up breaking their political contract and abuse their power for personal or departmental gain.  This type of corruption can involve only one officer, or it can involve a group of officers.  Internal police corruption is a challenge to public trust, cohesion of departmental policies, human rights and legal violations involving serious consequences.  Police corruption can take many forms.

Corruption in Mauritius: Corruption in Mauritius is a widespread and growing problem.  In cables leaked from the US embassy the problem with corruption was referred to as "pervasive and ingrained".  The Independent Commission Against Corruption (ICAC) investigates offenses and can confiscate the proceeds of corruption and money laundering.  In 2008, the Director of the Mauritius Customs service stated that stated that, during a meeting on April 11, 2008, with government officials, including the Financial Secretary of the Ministry of Finance and Economic Development and Deputy Commissioner of Police, he was told in no uncertain terms that he should remain quiet about the alleged corruption because if it were to become public, it could bring down the current government of Mauritius.  In 2013, Dutch dredging group Boskalis has been fined the equivalent of €1000 by a court in Mauritius for making illicit payments to a port official.  In February 2016, the outgoing United States ambassador to Mauritius stated that there is so much turmoil at the Independent Commission Against Corruption that it has lost its credibility.  In April 2016, the Independent Commission Against Corruption opened an investigation in the recruitment of the director of the Independent Broadcasting Authority (Mauritius).  In April 2016, the Independent Commission Against Corruption recommended formal proceedings against the former Minister of the Environment.  In May 2016, the representative of Cisco System filed suit against the National Computer Board and executives of the Mauritius Qualifications Authority.  It was alleged that a bribe is required for all government projects.

Mollen Commission: The Mollen Commission is formally known as The City of New York Commission to Investigate Allegations of Police Corruption and the Anti-Corruption Procedures of the Police Department.  Former judge Milton Mollen was appointed in June 1992 by then New York City mayor David N. Dinkins to investigate corruption in the New York City Police Department.  Mollen's mandate was to examine and investigate “the nature and extent of corruption in the Department; evaluate the departments procedures for preventing and detecting that corruption; and recommend changes and improvements to those procedures”.

Clemence B. Horrall: Clemence Brooks Horrall (September 24, 1895 – October 4, 1960) was Los Angeles Police Department Chief of Police from June 16, 1941, when he succeeded Arthur C. Hohmann to serve as the 41st Chief of the L.A.P.D., to June 28, 1949, when he resigned under pressure during a grand jury investigation of police corruption.  Clemence Brooks Horrall was born in Washington, Indiana and graduated from Washington State University.  Horrall had become chief when Hohmann, under pressure from Los Angeles Mayor Fletcher Bowron, voluntarily took a demotion to deputy chief after he had become ensnared in a police corruption trial that had embarrassed the mayor.

Bent Coppers: Bent Coppers: The Inside Story of Scotland Yard's Battle Against Police Corruption is a non-fiction book by award-winning British journalist Graeme McLagan.  First published in the United Kingdom in 2003 by Orion Publishing Group, the book examines police corruption within the Metropolitan Police Service and South Eastern Regional Crime Squad—with particular focus on the 1990s and early 2000s—and the establishment and activities of the force's anti-corruption "Ghost Squad".  Its publication led to a 4-year legal case resulting in a landmark ruling in English defamation law.

Knapp Commission: The Commission to Investigate Alleged Police Corruption (known informally as the Knapp Commission, after its chairman Whitman Knapp) was a five-member panel initially formed in April 1970 by Mayor John V. Lindsay to investigate corruption within the New York City Police Department.  The creation of the commission was largely a result of the publicity generated by the public revelations of police corruption made by Patrolman Frank Serpico and Sergeant David Durk.  The commission confirmed the existence of widespread corruption and made a number of recommendations.

Frank Serpico: Francesco Vincent Serpico (born April 14, 1936) is a former American New York City Police Department (NYPD) officer who holds both American and Italian citizenship.  He is known for whistleblowing on police corruption in the late 1960s and early 1970s, an act that prompted Mayor John V. Lindsay to appoint the landmark Knapp Commission to investigate the NYPD.  Much of Serpico's fame came after the release of the 1973 film "Serpico", which was based on the book by Peter Maas and which starred Al Pacino in the title role, for which Pacino was nominated for an Oscar.

Rampart scandal: The Rampart scandal refers to widespread police corruption in the Community Resources Against Street Hoodlums (CRASH) anti-gang unit of the LAPD's Rampart Division in the late 1990s.  More than 70 police officers either assigned to or associated with the Rampart CRASH unit were implicated in some form of misconduct, making it one of the most widespread cases of documented police corruption in United States history, responsible for a long list of offenses including unprovoked shootings, unprovoked beatings, planting of false evidence, stealing and dealing narcotics, bank robbery, perjury, and the covering up of evidence of these activities.

Robert Leuci: Robert Leuci (February 28, 1940 – October 12, 2015) was a detective with the New York City Police (NYPD), US, known for his work exposing corruption in the police department and the criminal justice system.  After retiring from the NYPD he wrote novels, short stories, TV episodes and a memoir of his years on the force.  He taught and had residencies at over forty universities and law schools, and lectured on morality and ethics erosion at many US police departments and the FBI academy in Quantico, Virginia.  Leuci knew Frank Serpico, known for being the first officer to expose corruption within the police department ranks.  The book (by Robert Daley) and the film "Prince of the City" are based on a portion of Leuci's police career.

Supporting paragraphs: Knapp Commission Frank Serpico
Answer: whistleblowing