Harold Shipman: Who was 'Doctor Death', how many of his patients did he kill and how was he finally caught?

The 20th anniversary of Harold Shipman's initial arrest is being marked by a new documentary exploring the crimes of Britain's most prolific serial killer.

The ITV programme, Harold Shipman: Doctor Death, promises new interviews with witnesses and investigating officers and footage of his interrogation by police in a bid to re-assess the mass murder case.

Shipman, a family GP working in Hyde, Manchester, is thought to have killed 218 patients with lethal injections of diamorphine between 1975 and 1998, when he was finally apprehended.

That death toll - 80 per cent of which is accounted for by elderly women - was placed by the Shipman Inquiry, which published its findings on his actions after a two-year probe in January 2005.

Investigators, however, believe the real total could be closer to 250.

Shipman was found guilty of 15 specimen murders by a jury at Preston Crown Court on 31 January 2000 and sentenced to life imprisonment.

He hanged himself in his cell at HM Prison Wakefield in Yorkshire on 13 January 2004, a day before his 58th birthday, allegedly so that his wife could cash in a £100,000 maximum pension payout.

Shipman was born on the working class Bestwood council estate in Nottingham in 1946, the son of a lorry driver, both of his parents devout Methodists.

He was a success at High Pavement Grammar School, which he attended after passing the 11-Plus, an accomplished rugby player and athlete and very close to his mother, Vera.

Harold witnessed her dying of lung cancer aged just 43 when he was 17, observing closely how a local doctor administering morphine was able to temporarily ease her pain and suffering.

He married farmer's daughter Primose May Oxtoby, with whom he would have four children, in 1966 and attended Leeds School of Medicine, where he graduated in 1970.

Having commenced his career as a junior doctor at Pontefract general infirmary, Shipman took his first post as a GP at the Abraham Ormerod Medical Centre in Todmorden, West Yorkshire.

Here he was caught forging prescriptions of Demerol for his own use in 1975, an offence for which he was fined £600 and required to attend a drug rehabilitation clinic in York.

After a short spell as a medical officer in Durham, he subsequently transferred to the Donneybrook Medical Centre in Hyde in 1977, where he would spend the next 15 years of his career before setting up a one-man practice in 1992.

Shipman quietly attended to his patients, becoming a well-known figure in the community as he deftly concealed his horrific poisoning agenda with calm and cunning.

Shipman always denied the accusations against him and refused to co-operate with criminal psychiatrists but the best guess as to the motive behind his crimes was his having developed a god complex regarding the "kill or cure" power he wielded over his infirm patients.

The mild-mannered "good doctor" was finally exposed as "The Angel of Death" after he was caught forging the will of Kathleen Grundy, Hyde's former mayor, when she passed away in June 1998, an attempt to defraud the widow's estate of £360,000.

This, combined with growing concerns about the abnormally high mortality rate at his practice, drew the attention of the authorities and, following the exhumation of Ms Grundy's body by coroners in August, Shipman's fate was sealed.

Harold Shipman: Doctor Death is broadcast on ITV at 9pm on Thursday 26 April