Teams of police officers and archaeologists descended on two properties in Brighton, East Sussex, armed with ground-penetrating radar and shovels.
They were searching for bodies or other evidence left by the 63-year-old when he lived at the addresses in the 1980s.
The move marked a dramatic escalation in a behind-the-scenes inquiry, dubbed Anagram, focusing on Tobin’s lifetime of crime and violence.
Police are convinced Tobin claimed more victims as he lived across Britain under different names and trawled the roads for vulnerable female hitchhikers.
Tobin was told last December he would die in jail after he was convicted of strangling 18-year-old Dinah McNicol.
The former church handyman was already serving life terms for the murders of 15-year-old Vicky Hamilton and Angelika Kluk, 23.
Police discovered their remains buried in the garden of a house in Margate, Kent, where Tobin moved to in March 1991.
Detective Chief Inspector Nick Sloan, of Sussex Police, said that officers must “satisfy themselves” that no crimes were committed at either property.
“It does appear that Tobin was fairly active at those addresses at those times. As long as there are lines of inquiry, we will continue. We have to consider the families of those who may have been one of his victims and it is imperative they find closure. We will strive to achieve this.”
Chief Insp Laurence Taylor said: “At the moment these are not crime scenes. We do not know what is going to be there.”
Police said the searches behind flats in Marine Parade, Brighton, and a hairdressing salon in Station Road, Portslade, could continue for a month.
The salons were once a cafe, Ye Olde Tea-room, run by Tobin in 1988 with his future wife, Cathy Wilson, and their baby son.
Neighbours recall Tobin doing a substantial amount of DIY as he converted it from a junk shop and cleared the garden.
Marine Parade is a large housing association block of flats which backs on to a small area of grass and concrete paving.
Investigators have refused to go into detail about why police were targeting the two properties or what cases they may be linked to.
Police responsible for the Anagram inquiry are believed to have narrowed down their review of unsolved murders and disappearances linked to Tobin to nine cases.
These may include the murders of art student Jessie Earl, 22, whose body was found in 1989, and Louise Kay, 18, who disappeared in Eastbourne in 1989. Her body has never been found.
There are several other possible cases including law student Pamela Exall, 22, who vanished in Norfolk in 1974, schoolgirl Patricia Morris, 14, who went missing in Essex in 1980, and Suzanne Lawrence, 14, last seen in Essex in 1979.
Other cases include the murders of three women in Glasgow in 1968 and 1969 by a figure nicknamed “Bible John” and the deaths of schoolgirls Karen Hadaway, 10, and Nicola Fellows, nine, in Brighton in 1986.
Detectives attempted to speak to Tobin in prison about the latest developments but he refused to talk to them and they remain keen to unravel further details of his life, particularly where he lived in 1977 and 1978.
The itinerant serial killer has lived in several other towns and cities, including Glasgow, Margate, Kent, and Havant, Hampshire. Police said he may have owned more than 100 vehicles and used 40 aliases.