A German nurse who admitted to killing at least 30 of his patients as part of a thrill-seeking game to see if he could revive them has apologised to the families of his victims.

The 38-year-old man, identified only as Niels H. was accused of killing three people and attempting to kill two others by injecting them with an overdose of heart medication. Prosecutors claimed he was motivated by the thrill of trying to resuscitate his victims.

However, during his trial in the northern city of Oldenburg, the defendant told the court he performed the procedure on at least 90 patients, causing over 30 deaths between 2003 and 2005.

Court spokesman Michael Herrmann told The Associated Press that the defendant would get bored after being moved from an emergency room to a new role.

"When a CPR occurred there he got a kick out of it and decided to actively bring about resuscitation cases in Delmenhorst," said Mr Herrmann.

Appearing in court this week, he apologised to relatives of the victims attending his trial. "He said he'd understand if they couldn't accept that,” said Mr Herrmann.

Police have since begun probing some 200 deaths that occurred during the man's time working in Delmenhorst, Oldenburg and Wilhelmshaven.

A verdict on the three murder charges is expected next week.