Charles Edmund Cullen (born February 22, 1960) is a former nurse who is the most prolific serial killer in New Jersey history and is suspected to be the most prolific serial killer in American history.
 He confessed to authorities that he killed up to 40 patients during the course of his 16-year nursing career.
 But in subsequent interviews with police, psychiatric professionals, and journalists Charles Graeber and Steve Kroft, it became clear that he had killed many more, whom he could not specifically remember by name, though he could often remember details of their case.
 Experts have estimated that Charles Cullen may ultimately be responsible for 400 deaths, which would make him the most prolific serial killer in American history.
A serial killer is a person who murders three or more people, in two or more separate events over a period of time, for primarily psychological reasons.
 There are gaps of time between the killings, which may range from a few hours to many years.
 This list shows serial killers from the 20th century to present day by number of victims.
 In many cases, the exact number of victims assigned to a serial killer is not known, and even if that person is convicted of a few, there can be the possibility that he/she killed many more.
My Brother the Serial Killer is a 2012 American television documentary about serial killer Glen Rogers, otherwise known as the "Casanova Killer", who was convicted for a series of murders and arsons.
 The documentary was narrated by Rogers' brother Clay Rogers and aired on Investigation Discovery in November 2012.
 "My Brother the Serial Killer" received widespread media attention for Clay's claims that his brother was responsible for the 1994 murders of Nicole Brown Simpson and Ronald Lyle Goldman.
Cold North Killers: Canadian Serial Murder is a 2012 Canadian non-fiction book written by Lee Mellor and published by Dundurn Press.
 It documents the lives of sixty Canadian serial killers, with the earliest being Edward H. Rulloff and the most recent being Russell Williams.
 The book uses Katherine Ramsland's interpretation of what constitutes a serial killer—someone who has killed at least two people on two separate occasions, and who attempted to or likely would have killed again—as outlined in her 2007 book "The Human Predator".
 "Cold North Killer's" own definition of what constitutes a Canadian serial killer includes both Canadians who committed murder abroad (such as Keith Hunter Jesperson and Gordon Stewart Northcott) and non-Canadians who committed murder in Canada (like William Dean Christenson and Earle Nelson).
The Kingdom of Huang (黄國) was a country that was first created during the Xia Dynasty (2070 BC – 1600 BC) and was restored again a second time in 891 BC during the time of the Zhou dynasty until the middle Spring and Autumn period, when it was annexed by the Kingdom of Chu in 648 BC.
 There were at least several dozen known monarchs in total of the Kingdom of Huang during the 1,400 years that this country existed.
Richard Leonard Kuklinski (April 11, 1935 – March 5, 2006) was an American contract killer and serial killer who was convicted of murdering five people, though he likely killed at least several dozen more.
 He was associated with members of the American Mafia, namely the DeCavalcante crime family of Newark, New Jersey, and the Five Families of New York City.
The Iceman is an American biography crime thriller film based on the true story of longtime notorious hitman Richard Kuklinski.
 Released in 2012 at the Venice Film Festival, the film was directed by Ariel Vromen, and stars Michael Shannon as Kuklinski, Winona Ryder, Chris Evans, and Ray Liotta.
Pedro Rodrigues Filho (born 17 June 1954 in Santa Rita do Sapucaí) is a Brazilian serial killer.
 Nicknamed Pedrinho Matador (Killer Petey) and arrested in 1973, in 2003 he was convicted of murdering at least 71 people and sentenced to 128 years in prison.
David Joseph Carpenter (born May 6, 1930), a.k.a. the Trailside Killer, is an American serial killer known for stalking and murdering his victims in State Parks in California.
 Carpenter killed several people on hiking trails near San Francisco, California.
 Carpenter killed at least 10 people, with one attempted victim, Steven Haertle, surviving.
 Carpenter used a .38 caliber handgun in all but one of the killings, with a .44 caliber handgun being used in the killing of Edna Kane on Mount Tamalpais.
Philip Carlo (April 18, 1949 – November 8, 2010) was a journalist and best selling biographer of Thomas Pitera, Richard Kuklinski, Anthony Casso, and Richard Ramirez.
 Carlo suffered from amyotrophic lateral sclerosis (ALS), commonly known as "Lou Gehrig's Disease".
 He was bound to a wheelchair and respirator, but retained his ability to speak normally during his lifetime.
 He died of the disease on November 8, 2010 at age 61.

Question: Philip Carlo, was a journalist and best selling biographer of Richard Kuklinski, he was an American contract killer and serial killer who was convicted of murdering how many people, though he likely killed at least several dozen more?
Answer: five