Former German hospital nurse Niels Hoegel has claimed to have killed around 100 of his patients with drug overdoses, which would make him one of the world's most prolific serial killers in recent history.
The verdict in his trial is due Thursday.
Here are some of the most notorious serial killers of the past decades.
Russia's most prolific
Siberian ex-policeman Mikhail Popkov was found guilty in December 2018, at the age of 54, of 56 murders. He was already in jail for 22 killings.
Between 1992 and 2007, he raped and killed women with an axe or hammer after offering them late-night rides, sometimes in his police car. He also killed a male policeman.
He is Russia's worst serial killer of recent times.
Samuel Little, a 78-year-old drifter, confessed in November 2018 to 90 murders between 1970 and 2005 and law enforcement authorities have corroborated more than 40 of them so far.
If all 90 confessions are confirmed, Little would be the most prolific known US serial killer.
The former boxer, arrested in 2012, targeted mainly drug addicts and prostitutes, many of whom were never identified. The FBI in February 2019 released 16 portraits drawn by him in an attempt to identify some of his victims.
Alexander Pichushkin was sentenced to life in prison in Moscow in 2007 for 48 murders, most between 2002 and 2006.
Aged 33 at his trial, Pichushkin said he wanted to kill one person for each of the 64 squares on a chessboard, and crossed out a square for every kill, hence his nickname.
His victims were mainly elderly alcoholic men he met in a park.
Yang Xinhai was executed in China in 2004, aged 35, after murdering 67 people in a three-year rampage that ended in 2003.
Characterised as an introverted drifter, he entered rural homes and sometimes slaughtered entire families with an axe, hammer or spade.
Police listed robbery and rape as motives but Yang was also described as a deranged killer who enjoyed what he was doing.
US 'Green River killer'
US truck painter Gary Ridgway confessed in 2003 to strangling 48 mainly prostitutes and runaways from 1982 to 1984, but he is suspected of more.
Nicknamed the "Green River Killer" after the Seattle waterway where his first victims were found, he was 54 years old when he was convicted and jailed.
England's 'Doctor Death'
Harold Shipman, a family doctor near Manchester, was sentenced to life in 2000 after being convicted of killing 15 of his elderly patients with fatal doses of morphine. He hanged himself in prison in 2004, aged 57.
An inquiry found that Shipman, nicknamed "Doctor Death", had killed around 250 patients between 1971 and 1998, making him the country's worst serial killer.
Luis Alfredo Garavito was jailed for 835 years in 2000, aged 42, for murdering 189 boys over a five-year span until 1996.
Known as "The Monster of Genova" after his birthplace in Colombia, Garavito gained access to his victims -- aged between eight and 16 -- by posing as a charity worker, salesman, monk or disabled person.
'Butcher of Rostov'
In 1992 Andrei Chikatilo, 56, was sentenced to death for 52 sexually motivated killings between 1978 and 1990.
The former teacher, known as the "Butcher of Rostov" after the area in southern Russia where he was particularly active, was executed in 1994.
'Monster of the Andes'
In 1980 Colombian Pedro Lopez Monsalve was arrested at a market in Ecuador after attempting to abduct a young girl. He later confessed to having strangled at least 310 children from poor backgrounds in Colombia, Ecuador and Peru.
The "Monster of the Andes" was sentenced to 16 years in prison in Ecuador and then extradited in 1994 to Colombia where he was interned in a psychiatric hospital.
Freed several years later, he disappeared and would today be in his 70s.
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