The nurse has been suspended on full pay from Bassetlaw general hospital, Nottinghamshire, since January. Police have so far conducted 1,870 interviews and taken 975 statements.
There was no reply yesterday at the nurse's home in Worksop, close to the hospital where she was appointed in 1992. She previously worked at Gloucestershire Royal hospital, Gloucester; Nottingham City; Southmead, Bristol; John Radcliffe, Oxford; St George's, south London; Central Middlesex, north-west London; and Northern General, Sheffield.
Hospital authorities last night opened telephone lines offering confidential advice to any patients or relatives of patients concerned.
``If we are looking at a case which involves a patient, that patient or their family will know,'' Detective Superintendent Peter Coles, leading the investigation, said yesterday.
The police were called in by management at Bassetlaw hospital in February, and have committed 21 officers to full time inquiries, plus civilian support staff to store data on computer files.
Det Supt Coles said the number of ``incidents'' involving alleged tampering with vital equipment on the Bassetlaw ward had risen to 30.
Initial inquiries by the police had indicated that breathing apparatus and pumps delivering medication intravenously to five patients may have been tampered with on 16 occasions between November 1993 and January. Two patients subsequently died, although their identities and causes of their deaths have not been disclosed.
Inquiries at other hospitals were continuing, but Det Supt Coles said he could not compromise the investigation by revealing how many additional incidents elsewhere had aroused police suspicions.
The nurse had not always been employed in intensive care. She worked in a kidney unit at the Gloucestershire Royal, and had no duties in intensive care at Nottingham City hospital.
``It is a very, very serious inquiry,'' Det Supt Coles said. ``The focus has been, and remains, Bassetlaw.''
Police angrily deny suggestions that the investigation has floundered, although nobody has been arrested or interviewed under caution.
The Crown Prosecution Service (CPS) had been closely involved since the outset of the inquiry, Det Supt Coles said. He denied that CPS lawyers had complained that evidence gathered could not sustain a prosecution with reasonable chances of a conviction.
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