The killing of patients in a care center scandal in Uruguay, which could number into the hundreds, may date back as far as 2010, according to the court testimony of one of the accused nurses.
Juan Ariel Acevedo, 46, told the court he did not remember how many times he injected patients to kill them. He is indicted for 10 murders.
The other nurse, Marcelo Pereira, 40, who is accused of five murders, said the killings had been going on for "a year or maybe a year and a half."
The nurses had treated patients for more than a decade, which raised fears the final death toll could rise and leading countless families to wonder if their relatives had died naturally or been murdered by their caregivers.
The judge said it was not determined if the pair acted alone, but Interior Minister Eduardo Bonomi has said in recent days both nurses knew what the other was doing, and described a "sort of competition" between them.
Police and health authorities meanwhile said they have received hundreds of enquiries from relatives of people who died in the two hospitals where the nurses worked, fearing their loved ones might have been victims.
Ines Massiotti, the defense attorney for Acevedo, 46, said Tuesday her client, claimed to kill the patients "so they would not have to suffer more."
But Massiotti said Pereira, by contrast, was "evil" and sought to kill the patients in disgust over their infirmities.
Police arrested the two nurses Sunday and charged them with murdering patients at a private Neurological Intensive Care Center and at a public hospital's intermediate-level care unit.
The health ministry on Tuesday opened a probe of hospital management with help from experts with the Pan American Health Organization (PAHO).
Health Minister Jorge Venegas on Monday described the suspects as "serial killers," and promised far-reaching inspections of both private and public medical facilities.