Detectives believe that at least three more women could have been killed by sadistic John Sweeney who has been convicted of murdering two former girlfriends.
Carpenter Sweeney cut up the bodies of Melissa Halstead and Paula Fields and threw the bits in canals in England and Holland.
Now police in both countries fear other former lovers met the same fate.
Sweeney also launched an axe attack at girlfriend nurse Delia Balmer who was only saved when a neighbour arrived to help.
He would boast of his woman-hating attacks in paintings and verse he wrote, the Old Bailey heard.
In one picture showing a bloody axe, he called himself the Scalp Hunter. In a poem he said he had fed Miss Halstead to the fish.
Liverpool-born Sweeney, 54, was found guilty of murdering Miss Halstead and Miss Fields, and perverting justice. He will be sentenced on Tuesday after refusing to leave the cells on Monday.
Now detectives want to know what happened to three other former girlfriends who have not been seen for many years.
A trainee nurse called Sue from Derbyshire was said to have gone to Switzerland in the late 1970s or early 1980s.
And they are also trying to trace two South American former girlfriends of Sweeney who have not been seen since the late 1990s.