Story highlights The two male nurses wanted to relieve patients' pain, an attorney says

They admitted to killing patients at Uruguayan hospitals, a judge says

A woman has been charged with being an accomplice in one of the killings

One patient died a day after his discharge order was signed, an official says

Two male nurses face murder charges in Uruguay after reportedly admitting to killing at least 16 patients in two hospitals in the country's capital.

One of the men has been charged with five aggravated homicides, while the other has been charged with 11 aggravated homicides, Judge Rolando Vomero said in an interview Sunday with CNN affiliate Teledoce, noting that the two men appeared to have acted independently of each other.

Authorities are also charging a woman as being an accomplice in one of the killings, he said.

According to the authorities, the two male nurses, ages 39 and 46, both said they killed the patients because they did not want to see them suffer.

"My client is fully conscious of his actions. He fully confessed in front of the judge (and) prosecutor, and his defense is that he did it out of mercy," said attorney Ines Massiotti.

The nurses wanted to relieve patients' pain, attorney Santiago Clavijo said.

"It wasn't a vicious operation in the spirit of death," he told reporters.

But apparently not all those killed were terminally ill. One patient had their discharge order signed one day before his death, said Interior Minister Eduardo Bonomi.

The killings took place at the hospitals of Maciel and La Espanola in Montevideo. One of the men worked in the neurosurgery department at La Espanola; the other worked in that same department, as well as in the cardiology ward at Maciel.

The police had been investigating suspicious deaths of patients at the hospitals for weeks after a tip from a worker at Maciel.

A recent death prompted the police to accelerate proceedings and provided them with enough evidence to make the arrests, Bonomi said.

Authorities say they believe the nurses killed the patients either by administering a morphine overdose or by injecting air bubbles into their blood stream.

The government has set up an office to provide support to the families of the victims, said Health Minister Jorge Venegas.