Story highlights A group of doctors allegedly altered oxygen levels for patients

Police: The doctors also administered lethal doses of medication

Seven other health care professionals have been charged in the case

A Brazilian doctor appeared in court for allegedly killing seven patients to free up hospital beds in the southeast city of Curitiba.

Virginia Helena Soares de Souza recruited a group of doctors to help administer lethal doses of anesthetics, sedatives and painkillers, according to authorities.

In addition, the group allegedly altered oxygen levels for patients, leading to deaths by asphyxiation, police said.

Seven other health care professionals have been charged in the case.

Prosecutors allege de Souza pulled the plug on victims against the wishes of patients and their families, and in so doing broke the law. She did that to free up beds in the ICU and clear up the "clutter" the patients were causing, according to police.

De Souza was arrested in February, but was later released until trial. Her court appearance Wednesday is part of mandated monthly appearances to avoid going back to jail.

Investigators say between 2006 and 2013, de Souza ordered medical professionals working under her at an intensive care unit to alter medication and oxygen levels.

In an interview with CNN affiliate TV Globo, Mario Lobato, the doctor tasked by the health ministry to investigate the case, said the number of deaths could be much higher.

He said his team is analyzing medical charts of more than 1,700 patients and interviewing more doctors.

During the seven years the incidents occurred, in cases where de Souza did not prescribe the drugs herself, she ordered other doctors to change mechanical ventilation devices, according to authorities. She allowed them access to medical records to issue prescriptions in her name, police said.

De Souza has pleaded not guilty.

Her lawyer, Elias Mattar Assad, said she will prove that her orders in the ICU were backed and justified by medical literature. Lobato, however, said some of the patients were awake and conscious moments before the drugs were administered.

CNN affiliate TV Record reported that the investigation began a year ago. In telephone recordings made with the consent of the justice department, de Souza ordered other medical doctors and employees to shut down some ventilation devices.

Euthanasia is considered a crime in Brazil.