A nurse who was convicted of killing patients in Germany with overdoses of heart medication is now believed to have killed at least 84 people - and the true scale of the killings could be larger, investigators said.

A German hospital nurse has begun a life sentence for murdering two patients who were victims of a suspected wider killing spree that he says claimed 30 lives.

A nurse in Germany has expressed regret for killing up to 30 patients by giving them an overdose of heart medication.