The suspect in two mass shootings in Maine that killed nearly 20 people late Wednesday is a member of the Army Reserve who enlisted more than 20 years ago, military officials said Thursday.

Maine authorities said at a news conference Thursday that 18 people were killed at two locations in Lewiston, the state’s second-largest city. More than a dozen others were injured, they said.

Federal and Maine authorities are still searching for the suspected shooter identified as Robert Card, who enlisted in the Army Reserve in December 2002 and was a petroleum supply specialist who had achieved the rank of sergeant first class, a spokesperson for the service said. He was assigned to the 3rd Battalion, 304th Infantry Regiment at a training facility in Saco, Maine.

A petroleum supply specialist supervises and manages the reception, storage and shipping of petroleum-based products. Soldiers in the role also put fuel in vehicles and aircraft and make certain it is being transported and handled safely, according to the Army.

The Army said Card, 40, had no combat deployments and received some decorations, including the Army Achievement Medal, Army Reserve Component Achievement Medal, Humanitarian Service Medal, National Defense Service Medal and Army Service Ribbon.

“He should be considered armed and dangerous. We believe he is someone who should not be approached,” said Col. William Ross of the Maine State Police.

Ross said Card has been charged with several counts of murder, and a warrant has been issued for his arrest. He added seven people died at the Just-In-Time Recreation bowling alley and eight people were killed at Schemengees Bar and Grille. Three victims died later at the hospital, the Maine State Police said Thursday.

Card was also a certified firearms instructor and had been dealing with mental health issues, according to The Associated Press. Card spent a couple of weeks in a mental health facility in the summer and said he’d been hearing voices telling him to carry out a shooting at the Saco base, the AP reported.

“The Army did not train [Robert] Card as a firearms instructor, nor did he serve in that capacity for the Army,” an Army spokesperson said. “We take matters such as this very seriously, and our primary concern is ensuring that all legal and appropriate actions are taken in accordance with our commitment to upholding the highest standards of conduct among our soldiers and civilian personnel.”

A U.S. official told the AP that commanders with the 3rd Battalion, 304th Infantry Regiment became concerned in mid-July that Card was acting erratically while the unit was training at the U.S. Military Academy at West Point, N.Y.

The official who spoke on condition of anonymity said military commanders became concerned about Card’s safety and asked for the police to be called. New York state police took Card to the Keller Army Community Hospital at West Point for evaluation, the official said.

“This is a very difficult time for the community of Lewiston,” Ross said. “It was a rough night last night … but we are committed to bringing [Card] to justice.”

Card was initially described by police as a person of interest in the shootings at the restaurant and bowling alley, but authorities clarified Thursday that he’s now the chief suspect because he’s been charged with murder.

Maine Department of Public Safety Commissioner Mike Sauschuck said investigators are not yet certain about a motive for the shootings and don’t have answers yet to questions about his mental health, and how he obtained a firearm.

“They are questions we are looking into now, but not questions we can answer,” he said.

Dr. John Alexander, chief medical officer Maine Central Health Care, said multiple injured victims are in critical condition and several remain in stable condition.

Authorities released security camera images of Card during the attacks, which show him carrying an assault-style rifle.