A man of 22 died in agony of dehydration after three days in a leading teaching hospital.
Kane Gorny was so desperate for a drink that he rang police to beg for their help.
They arrived on the ward only to be told by doctors that everything was under control.
The next day his mother Rita Cronin found him delirious and he died within hours.
She said nurses had failed to give him vital drugs which controlled fluid levels in his body. 'He was totally dependent on the nurses to help him and they totally betrayed him.'
"A person acts with criminal negligence with respect to a result or to a circumstance described by a statute defining an offense when he fails to perceive a substantial and unjustifiable risk that such result will occur or that such circumstance exists. The risk must be of such nature and degree that the failure to perceive it constitutes a gross deviation from the standard of care that a reasonable person would observe in the situation."
A Metropolitan Police spokesman said: 'Detectives from the Homicide and Serious Crime Command are investigating the death of Kane Gorny at St George's Hospital after this was referred to us by Westminster Coroner's Court.'
A spokesman for St George's Hospital said: 'We are extremely sorry about the death of Kane Gorny and understand the distress that this has caused to his family.
'A full investigation was carried out and new procedures introduced to ensure that
such a case cannot happen in future.
'We have written to the family to explain the actions that have been taken and to answer their concerns about Mr Gorny's care. The family has also been invited to meet with trust staff to discuss the case in detail.'
The tragedy emerged a week after a report into hundreds of deaths at Stafford Hospital revealed the appalling quality of care given by many of the nurses.
This week a task force called on nurses to sign a public pledge that they will treat everyone with compassion and dignity.
A total of 1,282,900 people in England have jobs with the NHS: 2 per cent of the 30 million people of working age.
Only the Chinese Army and the Indian State Railways are believed to employ more people — with 2.3 million and 1.5 million staff respectively — but both workforces represent a far smaller proportion of the national populations.
And they're not done yet.
John Reid, the Health Secretary, said he was delighted with the growth, but added that he was aware that more action was needed to tackle existing staff shortages.