An Air Force nurse has been charged with giving lethal amounts of medication to three terminally ill patients in his care, military officials said Tuesday.

Capt. Michael Fontana, 35, was formally charged in military court with deliberately giving three Wilford Hall Medical Center patients lethal amounts of medication, and with conduct unbecoming an officer for allegedly changing a medical document.

The Air Force began investigating after another staff member at the San Antonio hospital discovered irregularities in Fontana's administration of medications that may have resulted in the death of a terminally ill patient, Air Force spokesman David Smith said.

The investigation, which began in August, revealed that two other patients in Fontana's care may have received lethal amounts of medication. Fontana was removed from duty as soon as the irregularity was reported, Smith said.

Wilford Hall, at Lackland Air Force Base, is the Air Force's largest hospital. It primarily serves military personnel and retirees but provides emergency and trauma care to some civilians.

Relatives of Fontana's patients were notified of the investigation, Smith said, but he declined to provide any details about them, citing federal privacy laws.

An Article 32 hearing, the military equivalent to a grand jury proceeding, will be conducted in the next few weeks, and the commander will decide whether the case goes to court martial.

A call to Fontana's home was not immediately returned Tuesday.

As part of Congress' latest round of base closures and realignments, Wilford will become an outpatient surgical center only in 2011. Brooke Army Medical Center, across town at Fort Sam Houston, will expand and take in Wilford's other cases.