FOR almost 27 years, an inmate of the Ashworth Special Psychiatric Hospital in Merseyside has held a dark, terrible secret.

What did he do with the remains of his mother after he cut her to pieces with a hacksaw in his Hedge End home?

While memories of the horrific events of August 1981 have faded for many people, it's a mystery that retired Hampshire police officer Mike Southwell - who brought Daniel Rosenthal to justice - still wants solved. "I've always wanted him to answer that question, but I don't think he's ever going to. It's closure for me, it's the final tick in the box," the former chief superintendent said this week.

"It would give me a certain pleasure not to go up to Ashworth and ask him where he put his mother's remains, but to tell him, because that's the last thing he's got left over the case. In his twisted mind I think that he must feel that is still something."

It's likely to be a secret that Rosenthal, now aged 53, will take to his grave as he has never admitted to the brutal murder of his mother and father, despite being jailed for life after his sick plot was undone by clever detective work and forensic science.

The grisly saga began on August 11 when Rosenthal travelled from his bungalow home in Hedge End to Paris to visit his father. It's believed he went to persuade his father to give him money to fund his bizarre experiments that earned him the reputation as the "mad scientist".

Shrouded by overgrown bushes that grew in the gardens of the bungalow he lived the life of a hermit, shunning the outside world. The story goes that he cut up hundreds of chicks every week, experimenting on their brains and embryos, and dug funny holes in his garden with spoons. Milton Rosenthal, 65, was getting fed up with having a 27-year-old sponger son and almost certainly died because he refused to part with more cash.

It's believed Daniel smashed his father with a hammer and then locked himself in the bathroom for three hours and cold-bloodedly diced the body into pieces that could be hidden and carried away in plastic carrier bags.

Rosenthal calculated that if he could get rid of the body he could get away with murder as the live-in au pair girl would be too scared to tell police. The next day he drove out of Paris to a forest where he buried his father's remains.

He returned to Hedge End and waited for a holiday visit from his 60-year-old mother Leah, who was suffering from chronic multiple sclerosis. He probably had no intention of killing his mother, but she was about to give him a terrible shock.

On August 23, she telephoned her ex-husband to ask him how the visit from Danny had gone. The au pair told her Milton was missing. Rosenthal is believed to have killed his mother soon after her arrival at Hedge End because she was going to raise the alarm about his father. However, he did not know about the involvement of third person, a mutual friend of the separated couple, who contacted Eastleigh police when the pair both disappeared.

Rosenthal told police that his mother had left for London, but the officers were immediately suspicious that this was no ordinary missing person case and he was taken in for questioning.Mr Southwell, then a Detective Inspector who had only joined Bitterne CID five weeks earlier, phoned the Paris flat and spoke to the au pair who broke down in tears and told him she believed Rosenthal had killed his father.

He spent the next four days interviewing Rosenthal, who gave nothing away, except for the fact he disposed of the chicken's remains in black bags he bought from Wisebuys in Bitterne.

"He was the most difficult and unusual person I've ever dealt with. He was in another world - he wasn't listening to us. He wasn't interested in our questions, he was actually looking down at us as if to say You peasants, you're never going to catch me'.

"When we came out of the interview room I looked at my colleague Detective Sergeant John Phillips and we simultaneously nodded Yes, he's done it'."

Despite a widespread sea, air and land search, no trace of his mother was found. The detectives, now believing Rosenthal had got rid of dismembered bits of his mother, had to make legal history by convicting him of murder without a confession - or a body. Their greatest weapon was to be forensic science.

The house was filthy, but there was one room where the floor had been thoroughly scrubbed. On closer examination, there appeared to be dried blood in the cracks of the linoleum tiles. Other samples were also found on the sole of Daniel's shoes.

The forensic team established the blood was the same group as Leah's, who had been a donor while living in Southampton. Later the same day, a minute piece of human tissue and muscle was found in the hollow handle of the hacksaw - that too had the same blood group.

However, the biggest break through came a few weeks before the trial was due to start when a French farmer, 80 miles from Paris, found a black dustbin bag which contained the headless remains of a man. On the outside of the bag was a tiny stick-on price tag that read "Wisebuys Bitterne".

In a bizarre trial, Rosenthal didn't challenge the forensic evidence and claimed his parents had been killed by the CIA and FBI. A trial that was expected to last three weeks was all over within four days.

"When I retired I got hold of the psychiatrist and I asked him if there was any point me coming up and talking to Daniel to see if he would at last tell me what he did with his mother's remains," Mr Southwell said.

"He told me that Daniel had never admitted that he did it, he will not discuss it with anyone and the last person on Earth that he is going to talk to is the bloke who put him away.

"What worries me a little is that if he ever comes out and someone doesn't tell me, I always felt he was the type who would poison your water.

"The psychiatrist told me he would be recommending that Daniel is never released as he has made absolutely no progress. "