Officials say they will seek to prosecute the 15-year-old arrested in the mass shooting at Marshall County High School as an adult.

The teen, who has not been named because he is a juvenile, was taken into custody after the shooting at the school in Benton, where he is a student.

Two people were killed — Bailey Holt and Preston Cope, both 15. Eighteen others were injured.

The suspect was initially charged with two counts of murder and 12 counts of first-degree assault, according to Assistant County Attorney Jason Darnall, who is prosecuting the case. Authorities previously said the teen would be charged with murder and attempted murder.

"Assault first is a little easier to prove than attempted murder and it's the same penalty," Darnall said, adding the charges could change if the case goes before a grand jury.

The charges are in juvenile court, which is closed to the public and where the records are sealed under Kentucky law. Prosecutors will request a judge move the case to adult court, at which time the details would no longer be secret.

Darnall said that local attorneys already have reached out to the Office of the Commonwealth's Attorney to move his charges. They will file the paperwork once he makes an initial appearance in court, which has to happen by Thursday.

The latest on the shooting: What we know now: Marshall County High School shooting

The teen is being held at a regional juvenile jail in Paducah, Kentucky, about half an hour from the high school, authorities said, and he has been appointed an attorney.

Darnall declined to say whether the teen has a criminal history, saying he couldn't detail specific facts of the case. When asked if the teen was injured in the shooting, Darnall responded, "Not that I know of."

Information from The Associated Press was used in this report. Justin Sayers: 502-582-4252; jsayers@gannett.com; Twitter: @_JustinSayers. Support strong local journalism by subscribing today: www.courier-journal.com/justins.