A nurse accused of killing two elderly patients gave them potentially fatal drugs for "the excitement of trying to revive them", a court has heard.
Benjamin Geen denies 20 charges
Benjamin Geen, 25, accused of killing David Onley, 77, and Anthony Bateman, 67, at Horton General Hospital in Banbury in 2004, denies 20 charges.
Oxford Crown Court also heard 16 people nearly died from respiratory problems.
Mr Geen is charged with 18 counts of GBH with intent and administering noxious substances to endanger life.
The offences relate to "unusually high numbers of patients suffering respiratory arrests" following their admission to the hospital where Mr Geen worked, the court heard on Tuesday.
That sparked an internal investigation which found that on each occasion involving the 18 alleged victims, Mr Geen had been on duty in an accident and emergency unit.
When he was subsequently suspended and arrested on 9 February, 2004, officers found an old, used syringe in the pocket of Mr Geen's fleece.
Tests on the fleece later found traces of two drugs, both capable of causing respiratory failure, the prosecutor Michael Austin-Smith QC told the jury.
Mr Austin-Smith described one - a muscle relaxant used to paralyse patients during surgery - as "deadly in the wrong hands".
He said normal hospital procedure was for syringes to be disposed of after one use.
Grievous bodily harm
Mr Geen is accused of murdering Mr Onley, from Deddington, between 20 and 23 January in 2004, and Mr Bateman, from Banbury, on 6 January the same year.
He is also accused of causing grievous bodily harm with intent to harm patients David Long, David Nelson, Robert Robinson, Hilda Wigram, Walter Coates, John Moncur Thorburn, Sheila Gray-Snook, Jonathan Feltham, Harold Boss, Noreen Brooks, Arthur Marlow, Grace Vera Fox, Esther Jordan, Heinrich Zinram, Herline Probert and Timothy Stubbs between 4 December, 2003 and 5 February in 2004.
Mr Austin-Smith QC told the jurors he would seek to prove Mr Geen deliberately administered drugs or other substances to make his patients collapse so that he could try to revive them.
The case continues.