SERIAL killer Peter Tobin is said to be "at death's door" in hospital.

The 76-year-old, who is serving life sentences for the murders of Angelika Kluk, Vicky Hamilton and Dinah McNicol, is chained to his bed and refusing food and medication.

Tobin is said to be "frail, weak and at death's door", the Sunday Mail reports.

A source told the paper: "That's been said about him before but he seems to hang on.

"To the unsuspecting eye, he's just a sick old man in hospital but the killer's face is still there."

READ MORE: Serial killer Peter Tobin in hospital after falling unwell in prison

Tobin is suspected of more murders, and families have begged him to tell the truth before he dies.

Nicola Stork's sister Louise Kay disappeared from Eastbourne in 1988 and is strongly believed to be another of Tobin's victims.

Nicola said: "I don't want Tobin to die because it means we might never know but I've got no sympathy if he's in pain.

"If he dies without giving us information about Louise, then it probably means we'll never know what happened to her or where she is.

"I hope he will confess something or the police can go and speak to him to get it out of him."

Meanwhile, the parents of 22-year-old Jessie Earl, whose body was found in 1989 after she went missing in 1980, also believe Tobin killed her.

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Retired detective superintendent David Swindle, who caught Tobin, said: "If there's any humanity there, Tobin will give up the secrets of what happened to these other victims.

"There won't be any sympathy for him being in pain but, if indeed he is dying, it's the least he could do for these families."

A Scottish Prison Service spokesperson said: "We don't comment on individuals in our care."

Tobin, who has cancer, has been treated in hospital a number of times in recent years, including in February 2016 when he was taken to the city’s Royal Infirmary by ambulance after he reportedly collapsed in his cell.