An open verdict has been recorded on the death of a woman who died of an overdose of diamorphine in Skegness Hospital.
Police had been treating it as a case of murder, but there will now be no prosecution.
Elsie Armstrong died in February 2002 on her 77th birthday, while she was terminally ill with congestive cardiac failure.
She was being given the diamorphine for pain relief using a motorised syringe driver, which administers the drug slowly over a period of time.
Spilsby Coroner Stuart Fisher heard that some time between 2030 and 2230 GMT on the evening of her death the machine had been tampered with, giving Mrs Armstrong a massive overdose which led to her death just after midnight.
DNA testing on the equipment failed to produce any useful evidence.
In giving the open verdict at Horncastle Magistrates' Court, Mr Fisher said it was unsatisfactory because he had not got to the bottom of things, but there was no alternative.