Officials say they finally know what killed the twin children found in a Mount Hope apartment in December.

According to the medical examiner, someone smothered the 5-year-old siblings, and police say the investigation has been deemed a homicide. On Dec. 18, police say they received a call from the building at 240 E. 175th St. asking for help for the 5-year-old girl and boy. When they arrived with first responders, they say they found them both dead on the scene.

Police say the twins' father was not home when they died. The father was cooperating with police and the mother was taken to the hospital where officials say she was emotionally distraught. It's still unclear who may be responsible for smothering the children.

Authorities say the family never had a history of domestic violence in their home and the parents never had any run-ins with the administration for children's services.

No arrests have been made in the case.

News 12 learned Thursday the Bronx district attorney will convene a grand jury to decide what charges to pursue and against those who may be responsible.