It had been a normal scene. The two little girls had been playing on Seagate Beach in Arbroath, running, jumping, throwing stones and looking at the debris which left on the sand by the previous night's winds and heavy rain.

They spotted a black plastic bag and their curiosity got the better of them. They bent down and tried to open it and what they saw shocked them.

They may have been too young to fully appreciate the horror of their find but they knew it was serious enough to run the 100 yards home to tell their mum.

She telephoned the police and returned to the scene. Within a few minutes the atmosphere in Arbroath had dramatically changed.

CID officers pulled open the black plastic bag and out fell the hair of the woman at the centre of a macabre mystery.

While police will not call it a murder investigation until the cause of death has been identified and until all other distant possibilities have been discounted, it seems certain that the girls have sparked a major criminal investigation.

Throughout yesterday, as officers combed the beach for clues and forensic experts planned the operation to remove the head and the severed hand found further along the beach, so as not to lose any potentially vital evidence, the people of Arbroath looked on.

Those who live in the seafront homes gathered to exchange notes on what little information there was.

All were convinced the head and hand had been washed up on the high tide and that they had not been there on Monday night. Too many dog walkers would have spotted them. Those who know the tides suggested the head could have been swept in from the south.

John Carswell, 32, told of the discovery. He was working in a nearby house.

"I have a niece and a nephew so you always keep an eye out for kids," he said.

"I noticed the two young red-haired girls playing about on the sandy part of the beach, throwing stones and that sort of thing, when they started poking about in this bag, ripped a small bit open and then took off. I thought they had just gone home but they got their mum and she came back down with them.

"I thought it must be a puppy or something because that has happened before.

"When I saw them come back with their mother I asked her what was going on. She said the girls thought they had seen a head, and that she had called the police.

"Two police officers came down and walked about the beach before trying to get the bag open. I knew there was something wrong because they were using their radios and I thought they might simply be calling the RSPCA but once the CID came down it was obviously identified as a body part and the hair was flapping about. From then on police came all day."

Mr Carswell said his father, also John, had cleared debris from the beach on Monday night and had put it in a trailer and the police had now taken it away.

"The little girls looked OK," he said. "They didn't look like they had seen a severed head. I think they maybe just opened it a little bit."

Student Brydon Duff, 28, from Edinburgh said: "We could see the police looking at something inside a plastic bag and we could make out a head. It had long brown hair and we could make out what looked like a chin.

"It was very gruesome. We came away for a quick break and we witnessed something horrific. It was not how we hoped to remember Arbroath."

As the speculation continued last night, Tayside officers began the painstaking forensic process of trying to identify the woman.