Investigators say Zapata told an informant he planned to run a woman's car off the road as she drove her children to school and kidnap one of the kids. Then he allegedly planned to demand a $300,000 ransom, or else he would cut off two of the child's fingers and send them to the family.
Federal prosecutors said Zapata rented a storage garage where he claimed he would keep the child. He told the informant he had been involved in other kidnappings.
Prosecutors said the kidnapping had been planned for mid-March.
FBI officials and Westminster police arrested Zapata on March 16 near the family's home.
Zapata faces up to 20 years in prison if convicted.