An oxygen pipe like those which became blocked
The cause of some cases in which hospital oxygen tubes became blocked is more likely to be faulty equipment than sabotage, say police.
The investigation into a series of incidents at hospitals across the country has found a potential cause for the fault.
It is thought that removeable caps of needles used separately to insert intravenous lines into the patient could possibly lodge and block the oxygen tubes.
However, Essex Police, which is coordinating the investigation, says this potential problem does not provide "a satisfactory explanation" for all the cases.
Tony Clowes, a nine-year-old boy from Dagenham in Essex died after staff used a blocked pipe at Broomfield Hospital near Chelmsford in July.
Since then a further four incidents have been added to the investigation.
They are:
Other cases of blocked tubes have been reported at other hospitals, but none of these have been added to the Essex Police inquiry.
A spokesman for the force said on Monday: "It has been established that it is possible for caps of 'intravenous-giving sets' in clinical areas containing breathing system components to become accidentally lodged in these components.
"Although this is a situation relevant to some of the incidents under investigations, it does not necessarily provide a satisfactory explanation to all incidents.
The police have refused to say which of the incidents are still being investigated for signs of sabotage.
Detectives are working with the Medical Devices Agency (MDA) - responsible for the safety of medical equipment - to bring their finding to attention of medical staff.
The MDA has already issued a "hazard notice" warning people handling oxygen tubes to make sure they are clear before using them.