The teenager charged with capital murder in the Santa Fe High School shooting was taken into federal custody Monday morning and will be arraigned on new charges, his attorney said.

Federal agents arrived at the Galveston County Jail to take Dimitrios Pagourtzis, 18, into custody and have him arraigned at the federal courthouse in Galveston at 1 p.m.

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Pagourtzis' attorney, Katy-Marie Lyles, said federal authorities plan to bring two new charges against her client related to the May 18 shooting, including a firearm charge and another for having an explosive device.

Lyles said the federal charges were unexpected. Families of people killed in the 2018 shooting at Santa Fe High School were told in a March private meeting with federal officials, including Ryan Patrick, the U.S. attorney for the Southern District of Texas, that it was unlikely federal charges would be filed against Pagourtzis.

"We were absolutely shocked," Lyles said. "March 20th, they're saying, 'We're not going to pursue federal charges,' but then I guess Mr. Patrick consulted with his boss, so to speak, and I guess they decided to move forward with federal charges at this time."

Read More: Families: Feds not planning charges against alleged Santa Fe High shooter

Since the meeting with the U.S. attorney, victims and survivors' families began calling their U.S. elected representatives and rallying others in Galveston County to do the same. The families of all 23 people killed or injured in the shooting also planned a press conference for Sunday, which they canceled in hopes federal authorities would act in coming days.

John Barnes, a Santa Fe ISD police officer who was shot in the massacre, said the potential federal charges are an example of justice at work.

"Apparently, the right foot got in the right ass up there in Washington, D.C., so now he's getting charged," Barnes said.

Rosie Y. Stone, whose 17-year-old son Chris was killed, began sobbing when she got confirmation that the shooter would face federal charges.

"This is so awesome, it's finally coming," Stone said, pausing to catch her breath. "You don't know how much I've prayed for this. I'm so happy that everybody came together when we posted it out there. Everybody did their part to make this happen."

Galveston County District Attorney Jack Roady, who is prosecuting the state charges against Pagourtzis, said he did not have any information on the nature of the federal charges, but said they would not impact the state's case against the accused shooter going forward.

Pagourtzis, who was 17 at the time of the shooting, already is facing state charges for capital murder and aggravated assault against a public servant in the shooting that killed 10 people and wounded 13, including John Barnes, a Santa Fe Independent School District police officer. Pagourtzis faces life in prison with the possibility of parole after 40 years if convicted.

Nick Powell covers Galveston County for the Chronicle. Follow him on Twitter and send him tips at nick.powell@chron.com

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