Question: Who is a bestselling American writer known for his fictional and non-fictional accounts of police work in the United States, Joseph Wambaugh or Helen Zahavi?

Context articles: Obert Skye
Helen Zahavi
Gregory Powell (murderer)
Peggy Moreland
Cathy Scott
Law enforcement in Argentina
Kate Klise
Use of UAVs in law enforcement
The New Centurions (novel)
Joseph Wambaugh

Obert Skye is a bestselling American children's writer known for the "Leven Thumps" series, the "Pillage" trilogy,[1] and "The Creature from My Closet" series.
 He is also the author of "Witherwood Reform School" and "Beyond Foo".
Helen Zahavi (born 1966) is an English novelist and screenwriter born and educated in London.
 Her father was sent to Britain with the Polish Army during the Second World War and her mother's parents came from Odessa.
 Before becoming a writer Zahavi worked as a Russian translator, and has spent several years living in Paris.
Gregory Ulas "Greg" Powell (August 2, 1933 – August 12, 2012) was an American criminal who kidnapped Los Angeles Police Department Officers Ian Campbell and Karl Hettinger on the night of March 9, 1963.
 Assisted by accomplice Jimmy Lee "Youngblood" Smith, Powell took the officers to an onion field near Bakersfield, California, where Officer Campbell was fatally shot.
 Infamously known as the "Onion Field" Killer, Powell's story was depicted in Joseph Wambaugh's 1973 non-fiction book, "The Onion Field".
 The book was later made into a 1979 film adaptation of the same name in which Powell was portrayed by James Woods.
Peggy Morse, née Bozeman (born in Texas, United States) well known as Peggy Moreland is a "USA TODAY" and Waldenbooks bestselling American writer of over 40 romance novels since 1989.
 She also signed a novel with her married name Peggy Morse.
Cathleen "Cathy" Scott (born 1950s in San Diego, California) is a "Los Angeles Times" bestselling American true-crime writer and investigative journalist best known for penning the biographies and true crime books "The Killing of Tupac Shakur" and "The Murder of Biggie Smalls", both bestsellers in the United States and United Kingdom.
 She grew up in La Mesa, California and later moved to Mission Beach, California, where she was a single parent to a son, Raymond Somers Jr.
 Her hip-hop books are based on the drive-by shootings that killed the rappers six months apart in the midst of what has been called the West Coast-East Coast war.
 Each book is dedicated to the rappers' mothers.
In Argentina the most important law enforcement organization is the Argentine Federal Police (equivalent to the FBI in the USA) with jurisdiction in all Argentine territory.
 Most routine police work is carried out by provincial police forces (equivalent to state police in the United States).
 An exception of the capital city of Buenos Aires (a federal district), where the Argentine Federal Police works with Argentine Naval Prefecture (Coast Guard) and Buenos Aires City Police (Municipal police).
Catherine "Kate" Klise (born April 13 in 1963) is an American writer known for children's fiction.
 Many of her books are illustrated by her sister, M. Sarah Klise.
 Their popular "Regarding" series is presented in a scrapbook format, with letters, journal entries, and related ephemera telling the story.
 She is also known for her picture books as well as the bestselling 43 Old Cemetery Road series.
 Klise's first adult novel, "In the Bag", was released in 2012.
 She is a contributor to "The Huffington Post".
Unmanned aerial vehicles (UAVs) have been used for domestic police work in Canada and the United States; a dozen US police forces had applied for UAV permits by March 2013.
 Texas politician Jim Hightower has warned about potential privacy abuses from aerial surveillance.
 In 2013 the Seattle Police Department’s plan to deploy UAVs was scrapped after protests.
The New Centurions, written by Joseph Wambaugh, is a 1971 novel depicting the stresses of police work in Los Angeles, California in the early 1960s.
 The author wrote the novel, his first, while a working member of the Los Angeles Police Department.
 The novel became a film starring George C. Scott and Stacy Keach.
Joseph Aloysius Wambaugh, Jr. (born January 22, 1937) is a bestselling American writer known for his fictional and non-fictional accounts of police work in the United States.
 Several of his first novels were set in Los Angeles, California, and its surroundings, and featured Los Angeles police officers as protagonists.