A German nurse who admits to killing more than 30 patients expressed regret for his actions Thursday, telling victims' relatives that he hoped his conviction would help them come to terms with their loss.

Prosecutors had accused the 38-year-old defendant of killing three people and attempting to kill two others by injecting them with an overdose of heart medication. They said he was motivated by the thrill of trying to resuscitate his victims.

But during his trial in the northern city of Oldenburg the man, identified only as Niels H. in line with German privacy rules, told the court that he performed the procedure on at least 90 patients, causing over 30 deaths between 2003 and 2005.

A spokesman for the Oldenburg regional court said the defendant had become bored after being moved from the city hospital's busy emergency room to a quieter post in the nearby town of Delmenhorst.

"When a CPR occurred there he got a kick out of it and decided to actively bring about resuscitation cases in Delmenhorst," court spokesman Michael Herrmann told The Associated Press by telephone.

The defendant apologized to victims' relatives, who were in court as co-plaintiffs, said Herrmann, who added: "He said he'd understand if they couldn't accept that."

A verdict is expected next week. Prosecutors are seeking a life sentence.

Questions have been raised about possible failures by the hospitals involved, and by law enforcement officials who initially charged him with just one count of attempted homicide in 2005. The defendant was eventually convicted of attempted murder in 2008 and sentenced to 7 1/2 years in prison before further cases came to light.

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