Lisburn magistrates court in Northern Ireland heard that the youth had been charged with possessing an assault rifle and 26 rounds of .762 calibre ammunition.
He had been charged on Monday with murder and possessing a firearm with intent to endanger life and with collecting information that could be of use to terrorists.
He was also charged with being a member of the Continuity IRA (Irish Republican Army) – a banned republican group which said it had killed Carroll.
The youth was remanded in custody and will appear on a video link at a court in Craigavon at the beginning of April.
Carroll was shot dead while on an emergency call, two days after two British soldiers were shot dead outside the Massereene army barracks in Antrim, Northern Ireland.
The killings have led to fears that fragile stability across Northern Ireland since the 1998 Good Friday peace agreement between Irish Republicans and Unionists allied to Britain could be in danger.
The attacks were roundly condemned by mainstream politicians in Belfast, London and Dublin.
Four people remain in custody over the March 7 killings, claimed by the Real IRA, another dissident Republican group.