The sister of a woman allegedly murdered by senior nurse Ann Grigg-Booth today condemned her as "evil".

Amy Newman's sister Eva Blackburn was one of three elderly patients at Airedale General Hospital, Steeton, whom Grigg-Booth was charged with murdering.

But Mrs Newman said the death of the former night matron had now robbed her family of the chance to find out why she could have killed the 75-year-old widow.

Mrs Blackburn died with her family at her side within 24 hours of being admitted to the Steeton hospital in November 2001.

Mrs Newman, of Cullingworth, said: "I've never been glad that someone has died before, but I am in this case. She must have had a reason for taking these lives, but I don't understand. She might have been evil, that's all you can say."

Grigg-Booth, 52, was to stand trial for the murder of Mrs Blackburn, Jane Driver, and Annie Midgley at the Steeton hospital between July 2000 and July 2002, and for the attempted murder of Michael Parker, 42, in June 2002.

She also faced 13 charges of administering noxious substances to 12 other patients between June 2000 and July 2002.

The charges related to her injecting patients with high doses of painkilling drugs such as morphine and diamorphine while working on the night shift.

She was charged in September 2004 and her trial was due to take place at Leeds Crown Court in April next year.

Grigg-Booth was found dead at her home in Nelson, Lancashire, on Monday. Police said there were no suspicious circumstances. A post-mortem examination was carried out last night.

Mrs Newham, 83, said bingo-loving Eva and their sister Ivy, 75, were very close and they missed her a great deal.

"We had a brother too and people used to call us the Brontes, just like them.

"Eva was a smashing person and tough as old boots. She was hardly ever poorly. When she was put on a drip just before she died she said 'I was fine until the buggers put this in me'."

Mrs Newham also compared Grigg-Booth to Harold Shipman, the GP who murdered his elderly patients by giving them drug overdoses.

"What I want to know is, how do people like that nurse get these drugs when they're not doctors? Surely someone must check on the drugs supply to see what's been used."

Detective Superintendent Phil Sedgwick, who led the West Yorkshire Police investigation, said it would probably be never known how many people Grigg-Booth had killed. Detectives had investigated dozens of patients' deaths where Grigg-Booth was involved in their care.

"We just don't know. Now we'll never know for sure," he said.

Det Supt Sedgwick said in interviews Grigg-Booth, who stood 6ft tall, was confident and even friendly.

"She came across as a very strong person and was chatty, but she always denied the charges and was not prepared to admit that she had broken the law.

"The police and the Crown Prosecution Service believe she committed these offences but there will not be the chance to prove that in court.

"All the victims' families have been spoken to or are in the process of being spoken to by family liaison officers."

Det Supt Sedgwick said his team suspected Grigg-Booth had used class A drugs, but she strongly denied having done so.

He added: "It was never established why she carried out the acts. You could theorise about it, but that's all it would ever be. Perhaps it was similar to Shipman and it was about power."

But staff nurse Gwyneth Trout, who worked with Ann Grigg-Booth, told of her disbelief about the charges against her.

Mrs Trout, 45, was given pethadone in June 2002 by Grigg-Booth while she was waiting to see a doctor for abdominal pains but she does not believe she was trying to poison her.

She was one of the patients to whom Grigg-Booth was charged with administering noxious substances.

Mrs Trout, of Greystones Mount, Keighley, said: "As a nurse you have to receive special training to give intravenous opiates that are injected into the veins and I assumed she had been given that as she always gave it."

She added: "She was trying her best to ease the pain - not for once did I think she was doing anything to harm me. I'd be shocked in those were her intentions. It's not something I would ever have imagined."

Mrs Trout had hoped the trial would shed light on the incident.

She said: "I was waiting for the trial and hoped that would clear things up. But now I will always wonder what happened that night. Now I will never know. I really feel for the families - they need answers."

Mrs Trout said she was shocked to hear of Grigg-Booth's death yesterday.

She said: "When I heard the news my immediate thought was that she had taken her own life. She looked awful in the pictures in the papers and on television. I'm not sure what happened whether the stress could have got to her or whether it was other circumstances. Normally she looked so bright."

Mrs Trout had worked with her from 1997 until she was suspended.

She said: "A lot of people felt intimidated by her - she had this aura about her. She was a very tall lady and the type who did not stand nonsense."