Question: How many homicides did a serial killer confess to before his execution and were investigated by Robert D. Keppel?

Context paragraphs:
Ted Bundy: Theodore Robert Bundy (born Theodore Robert Cowell; November 24, 1946 – January 24, 1989) was an American serial killer, kidnapper, rapist, burglar and necrophile who assaulted and murdered numerous young women and girls during the 1970s, and possibly earlier.  Shortly before his execution—after more than a decade of denials—he confessed to 30 homicides committed in seven states between 1974 and 1978.  The true victim count remains unknown, and could be much higher.

Internet homicide: Internet homicide refers to a killing in which victim and perpetrator met online, in some cases having known each other previously only through the Internet.  Also Internet killer is an appellation found in media reports for a person who broadcasts the crime of murder online or who murders a victim met through the Internet.  The first known murder of a victim met online was in 1996.  Depending on the venue used, other terms used in the media are Internet chat room killer, Craigslist killer, Facebook serial killer.  Internet homicide can also be part of an Internet suicide pact or consensual homicide.  Some commentators believe that reports on these homicides have overemphasized their connection to the Internet.

HMS Keppel (D84): HMS "Keppel" was a Thornycroft type flotilla leader built for the Royal Navy at the end of the First World War.  She was completed too late to serve in that conflict, but saw extensive service in the inter war years and in World War II.  She was an effective convoy escort and U-boat killer, being credited with the destruction of five U-boats during the Battle of the Atlantic.  She was the second of three ships named for 18th century Admiral Augustus Keppel.

Charles Cullen: 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.

Luis Garavito: Luis Alfredo Garavito Cubillos, also known as "La Bestia" ("The Beast") or "Tribilín" (named after Disney character "Goofy"'s Latin American Spanish name) is a Colombian rapist and serial killer.  In 1999, he admitted to the rape, torture and murder of 147 young boys.  His victims, based on the locations of skeletons listed on maps that Garavito drew in prison, could eventually exceed 300; Garavito continues to confess to more murders.  He has been described by local media as "the world's worst serial killer".  According to the Attorney General's Office and various judicial bodies, Luis Alfredo Garavito is the "second serial killer of the world."  Likewise, the judicial body ruled that all Garavito's sentences total 1853 years and nine days in jail.

Homicide Investigation Tracking System: Homicide Investigation Tracking System (HITS) is a violent crime database program of the Washington State Office of the Attorney General.  The system tracks homicides and rapes in and/or relating to the states of Washington and Oregon and also receives data from at least three other states and Canada.  The database provides information on over 6,000 murders and over 7,000 sexual assaults to local law enforcement agencies as well as advice and assistance in ongoing investigations.  Notable cases that have been assisted by HITS include Gary Ridgway (also known as the Green River Killer), John Allen Muhammad and Lee Boyd Malvo (the Beltway snipers), and serial killer Robert Lee Yates.

Holiday (comics): Holiday or the Holiday Killer is a fictional character appearing in the Batman story "" (1996-1997) by writer Jeph Loeb and artist Tim Sale.  The character is a serial killer who kills members of Gotham City's mobsters and corrupt officials on major holidays.  The true identity of the killer is never definitively revealed in the story itself; both Alberto Falcone and Gilda Dent confess to being Holiday, with Gilda claiming she committed the first three murders and that her husband Harvey took over subsequently.

My Brother the Serial Killer: 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.

David Meirhofer: David G. Meirhofer (June 8, 1949 – September 29, 1974) was an American serial killer who committed four murders in rural Montana between 1967 and 1974 — three of them children.  At the time, the Federal Bureau of Investigation was developing a new method of tracking killers called offender profiling, and Meirhofer was the first serial killer to be investigated using the technique.  Offender profiling is a method used to learn clues about the characteristics of an unknown killer from evidence at the scene of the crime and establish their behavioural patterns before they reach the height of their criminality.

Robert D. Keppel: Robert David Keppel (born 15 June 1944) is a retired American law enforcement officer and detective best known for his work investigating serial killers Ted Bundy and Gary Ridgway.

Supporting paragraphs: Robert D. Keppel Ted Bundy
Answer: 30 homicides