Serial killer Peter Tobin was today told he would die in jail as a senior detective asked: "Who knows if he has killed others?"

The murderer, who lived in Brighton in the late 1960s and early 1970s, was labelled "pure evil" as police trawled unsolved crimes in an attempt to reveal the full horror of his criminal past.

Jurors took 13 minutes to find 63-year-old Tobin, - already serving life terms for the murders of 15-year-old Vicky Hamilton and Angelika Kluk, 23 - guilty of strangling 18-year-old Dinah McNicol.

And police tonight pledged to “leave no stone unturned” in looking at crimes across the county to establish if he was responsible.

Vicky's father, Michael, sat near Miss McNicol's father, Ian, as jurors returned their verdict.

"I'm glad he's going to be in prison for the rest of his life," he said. "I hope he lives to be 100."

Tobin, from Johnstone, Renfrewshire, was jailed after a three-day trial at Chelmsford Crown Court.

As Tobin was led from the dock, a friend of the McNicol family showed him a hand-written sign which read: "May all your dreams be nightmares."

Miss McNicol was the second teenager Tobin murdered in 1991 - less than 18 months after the break-up of his marriage to wife Cathy, who he married in Brighton in 1969.

She vanished in August while hitchhiking to her home in Tillingham, Essex, after leaving a music festival in Liphook, Hampshire.

Six months earlier, Vicky disappeared while waiting for a bus close to Tobin's then home in Bathgate, near Edinburgh.

Detectives investigating the girls' disappearances focused their attention on Tobin after he was convicted of killing Miss Kluk - a Polish student staying at a room in a Glasgow church - in May 2007.

They discovered the remains of Vicky and Miss McNicol buried in the garden of a house in Margate, Kent, where Tobin moved to in March 1991.

"Rarely matters come before courts in this country that demonstrate human behaviour that is so self-serving and evil," said Detective Superintendent Tim Wills, who led the inquiry into Miss McNicol's murder.

"Peter Tobin I can only describe as pure evil."

And the detective who set up the nationwide inquiry into Tobin's background said police across Britain would leave "no stone unturned".

"Peter Tobin has now been found guilty of the brutal murders of three young women," said Detective Superintendent David Swindle. "Who knows if he has killed others?"

He added: "No stone will be left unturned and every single piece of information gathered will be investigated by forces throughout the UK to establish if he was responsible for any other crimes."

Trial judge Mr Justice Calvert-Smith imposed a whole life jail term on Tobin and told him: "This is the third time you have stood in the dock for murder. On all three occasions the evidence against you was overwhelming. Yet even now you refuse to come to terms with your guilt."

Outside court, Miss McNicol's half-sister Sara Tizard said: "After all these years, we at last know the truth and justice has prevailed."

Miss McNicol's father said nothing but nodded when asked if his nightmare was over.