SAN ANTONIO—A 14-year-old boy charged in the fatal shooting of a younger teen outside a South Texas home must remain in custody.

A judge in San Antonio on Tuesday ordered the suspect to remain in juvenile custody. Investigators say the suspect was already held on an unrelated robbery charge from a November incident when he was charged Monday with murder.

The case involves the drive-by shooting of 13-year-old Gabriel Martinez as he stood outside his family's San Antonio home before dawn on Sept. 15. Police are trying to determine a motive for the attack.

Police have said the victim was shot several times, collapsed and died.