Castillo originally told police someone kidnapped the toddler. Investigators say Tkachik told police Castillo beat the toddler after a potty training accident and that he helped dispose of the body.
Not guilty pleas were entered for both suspects in court Monday.
Lake County Sheriff's Department spokesman Mike Higgins says Tkachik was Tasered Monday after he climbed onto a table in a holding cell and refused to get down.
Jada was the subject of a 10-day search after Castillo said she disappeared from a car while the baby-sitting teenager went into a Gary convenience store.
The Associated Press contributed to this report.
