Murder charges were filed against two male nurses Sunday and a female nurse was charged with covering up a crime in a case involving more than a dozen deaths at two Uruguayan hospitals, judicial officials said.
The judge overseeing the case said there was no indication the two male nurses were acting together.
Judge Rolando Vomero said after a court hearing that the accused admitted to causing a total of 16 deaths of patients, but added that the investigation continued and the number was not final.
He said most of the apparent victims "were not terminally ill." He said they were injected with overdoses of morphine or aid to "cause death within minutes."
Vomero said one male nurse who worked at both hospitals admitted being involved in five induced deaths, and the other to 11 deaths in one hospital.
The judge said that from the evidence gathered so far, it "does not appear that there were any connections" between the two nurses "even though they both worked at the same place."
No further information was released on the three accused nurses because none had a criminal record.
Lawyer Ines Massioti, representing one of the nurses charged with "especially aggravated murder," told reporters that the judge had ruled the suspects could be held in jail while the investigation proceeds.
Massioti said her client acted "out of pity."
"After 20 years of working in intensive care, with stress and in contact with death, he could not stand it anymore," the lawyer said.
Earlier in the day, police inspector Jose Luis Roldan said officials were investigating suspicions that some hospital workers had given poison to patients who were in critical condition at the two hospitals.
Roldan said the allegations center on the private Sociedad Espanola hospital and the public Maciel Hospital. Officials at both declined to comment.
The South American country's Public Health Ministry issued a statement saying it was cooperating with the investigation into "presumed criminal acts linked to the health area." It gave no details about the allegations, but said it was conducting its own investigation and expressed "profound concern."