Serial child killer Robert Black who murdered four schoolgirls in the 1980s died from a heart attack, an inquest jury has confirmed.

The former delivery driver from Falkirk, central Scotland, who preyed on victims as young as five, was at serious risk after a lifetime of little exercise and heavy smoking.

Black was found dead in his high-security prison cell in Co Antrim three-years ago aged 68.

Jurors found he had died from a cardiac arrest, with degeneration of the walls of the coronary artery a secondary cause.

They confirmed underlying factors included his age, his smoking and diet, high blood pressure, a previous stroke and diabetes.

The jurors said there were no defects in his treatment by the health authorities or in the systems used by the Northern Ireland Prison Service which contributed to his death.

Black used tobacco until the end despite complaining of angina chest pains, doctors told his inquest.

High blood cholesterol caused narrowed arteries, a GP and a pathologist previously told the inquest hearing in Armagh.

For 51 years, Black regularly smoked 25g of hand-rolled tobacco and he had suffered a stroke 20 years before his death.

In 2011 the killer was convicted of sexually assaulting and murdering nine-year-old Co Antrim schoolgirl Jennifer Cardy in 1981 and dumping her body in a dam.

Jennifer, from Ballinderry, was abducted while she cycled to a friend's house near her home.

None of Black's family members could be traced by the Coroner's Service and were not at the inquest, Coroner McGurgan said.

His victims' relatives also stayed away.

The killer was serving a number of life imprisonment sentences when he died.

In May 1994, he was convicted of kidnapping, raping and murdering three of his victims.

Susan Maxwell was 11 when abducted in 1982 near the border between Scotland and England. Her body was gagged and bound and she was found 250 miles away in England.

His next victim five-year-old Caroline Hogg, who was abducted from Portobello in Edinburgh in 1983 and her body was found 300 miles away.

Sarah Harper, aged 10, was abducted in 1986 and found dead in the River Trent near Nottingham.