TAMPA, Fla. (Reuters) – A federal grand jury has indicted on 22 criminal counts an Iraq war veteran suspected of killing five people in a mass shooting at a Florida airport this month, U.S. prosecutors said on Thursday.

Esteban Santiago, 26, is accused of opening fire in the baggage claim area of the Fort Lauderdale airport on Jan. 6. The charges against him include multiple counts of violence at an airport resulting in death and injury, as well as firearms crimes.

If convicted, he could be punished by life imprisonment or death. The U.S. Attorney General has not decided whether to seek a death sentence, the prosecutors office said.

The indictment was returned by a federal grand jury in Broward County, Florida, where the attack occurred, prosecutors in the U.S. Southern District of Florida said in a news release.

Authorities said Santiago aimed at victims’ heads and bodies until he ran out of ammunition and was taken into custody. Five people were killed in the attack and six others wounded.

The indictment accuses Santiago of “substantial planning and premeditation to cause the death of a person.”

The attack was the latest in a series of deadly U.S. mass shootings, some inspired by Islamist militants, others carried out by loners or the mentally disturbed.

Santiago had a history of erratic behavior. Authorities have said they were investigating whether mental illness played a role in the shooting.

Court records show he is being represented by a public defender. A representative answering calls for the office said it had no immediate comment.

An arraignment hearing in Santiago’s case is scheduled in federal court in Fort Lauderdale on Monday.

A private first class in the National Guard who served in Iraq from 2010 to 2011, Santiago traveled from Alaska to Florida on a one-way airline ticket with a handgun and ammunition in his checked luggage, according to authorities.

Upon arrival, he claimed his gun case and loaded the weapon in a men’s bathroom, investigators said in a criminal complaint. He opened fire on the first people he saw after leaving the restroom, it said.

Santiago told investigators he was inspired by Islamic State and had previously chatted online with Islamist extremists, according to FBI testimony presented in court.

(Reporting by Letitia Stein; Editing by Colleen Jenkins and James Dalgleish)