POLICE investigating the murder of Miss Anne Cook have been inundated with calls following an appeal from the victim's twin sister but have no clear leads in the hunt for her killer.

Miss Cook, 35, who lived with her parents, Peter, 72, and Margaret, 70, in Widgeon Way, Watford, was killed by a single stab wound at about 6pm on Tuesday of last week as she walked her dog in Munden Drive, near the A41.

Her twin sister, Mrs Susan Curtler, appeared in front of television cameras and radio microphones at county police headquarters in Welwyn Garden City on Tuesday to appeal for information to help police solve the murder.

Describing her twin as 'a beautiful, gentle and loving sister', Mrs Curtler broke down as she made an emotional plea for information.

But despite her appeal producing dozens of calls from the public, no clear leads have been found.

Detective Superintendent Les Bolland, who is leading the investigation, said: 'If somebody has killed once, they have the potential to kill again. That is why we would urge anybody with information to come forward.

'The response from the public has been marvellous but we still need more people to come forward. No matter how unimportant it seems, it may be useful to us.'

On Monday officers searched the central reservation of the M1 after motorists called to say a man had run across the motorway from the Meriden estate near the time of the killing.

But the search failed to produce new evidence and police have not found the murder weapon, which is believed to be a knife with a blade larger than that of a penknife.

There are now 200 officers on the case. They are continuing door-to-door inquiries on the Meriden estate and will extend these to other areas if necessary.

The possibility of a link with other crimes is being investigated.

On April 7, two 11-year-old girls were sexually assaulted in Little Mundens, close to the murder scene.

Officers have been in contact with police in Cornwall, where two women were murdered in similar circumstances recently, but there is no evidence to suggest a connection.

Miss Cook had never married and did not have a partner at the time of her death. Police have been in contact with former partners and are investigating calls made from Miss Cook's mobile telephone, which she is known to have been carrying when she was killed.

A bare-chested man seen in the area has not been traced and officers are anxious to contact him.

He is white, in his mid-20's, 5ft 7ins to 5ft 11ins tall and of slim build. He has mousy, brown hair and a thin, angular face. He was carrying a white T-shirt and wearing jeans.

Police want to hear from anybody who saw a man fitting that description in the area, in particular between the M1, Westlea Avenue, Butterwick and The Gossamers, between 1pm and 8pm on the day of the murder.

Mr Bolland said: 'The man who carried out this attack might have thrown items of clothing into nearby gardens, so anyone who lives on or around the Meriden Estate who finds anything like this is urged to contact us.

'The attacker might also have had scratches on his chest and arms, consistent with running through undergrowth.

'It is important for anyone who knows of someone with such scratches to contact us.'

Mr Bolland also appealed to people to report anybody acting suspiciously on the day of the killing or afterwards.

This week Miss Cook's family have been struggling to come to terms with their loss.

Speaking at Tuesday's press conference, Mrs Curtler said: 'I really wish I didn't need to be here. I never imagined I would lose Anne, let alone in such a brutal way.

'We were closer than sisters could ever be. We grew up together and we shared everything. Now a big part of me has been cruelly taken away.

'Whoever did this to my beautiful, gentle, loving sister cannot begin to imagine the pain our family is going through.

'Her death has left all of us shattered and I am broken-hearted.

'She was wary of strangers and I know she would have put up a fight. Anne's dog Elvy knows something's terribly wrong and he's pining for her. If he could talk he'd be able to tell us what happened. He can't talk but someone else can.

'Please, please, if you know anything at all, no matter how small or insignificant you think it might be, contact the police now before it happens to someone else.'

Miss Cook was a bridesmaid at her twin sister's marriage to Mr David Curtler last August.

Mr Curtler said: 'Susan always told me that if I married her I would be marrying both of them.

'We're a very close family and though she kept herself to herself, she was very confident and a lovely person who wouldn't have hurt anyone.

'We're very angry about how she died and whoever did this needs to be caught quickly.'

Miss Cook had worked for 14 years for a Surrey-based company as an Internet web page designer before being made redundant. After that she worked as a temporary secretary.

Miss Cook also leaves two brothers: Martin, 47, who lives in Thatcham, Berkshire, and Colin, 44, who lives in Bedfordshire.

Anybody with information that may help the police is urged to contact the incident room on 01707 354449.