Probe after grim find.
The girls made the grim discovery in Arbroath, eastern Scotland, yesterday morning.
Police have been studying files of missing people trying to identify the woman.
Police later recovered a hand from the beach, which is popular with dog walkers.
Forensic officers have been combing the beach.
The sisters, from the Arbroath area, were playing during their Easter school holidays when they discovered the head.
Neighbours said they heard their screams before they rushed home and told their mother who called the police.
Residents of the seaside town said they were shocked at the gruesome find.
One said that when her son told her the news she thought it was an April Fool's joke. Linda Sloan, 48, added: "It is disgusting for something like this to happen. My kids play on that beach.
"It's those wee kids I feel sorry for, it's terrible what they must be going through."