The death of 8-month-old King Jay Davila has been ruled a homicide by "blunt force injuries," the Bexar County Medical Examiner's Office said Friday. The ruling comes three weeks after San Antonio police found King Jay's body in a backpack buried in an open field near the home of the baby's father, Christopher Davila. On Jan. 10, Christopher Davila, 34, admitted to detectives he buried his son and took investigators to the burial site, which is less than a mile from his last known address in the 5800 block of Castle Brook Drive. RELATED: Discovery of King Jay Davila's body 'a sad day for everybody,' FBI official says Christopher Davila claimed he was at home playing video games with King Jay on his bed in a car seat but not strapped in. He claims when he sat on the bed, the car seat fell to the floor with King Jay, causing his son to land face-first on the floor, according to an arrest affidavit. A large bump began to form over the baby's eye and Christopher Davila said he was afraid to call 911. He said when he checked on King Jay a few hours later, his son was dead, according to the affidavit. Police said a witness came forward to detectives, telling them that he heard King Jay crying Jan. 3. The next morning, the witness said he saw Christopher Davila carrying his son in the baby's car seat, which is the same day, police said, Christopher Davila carried out a staged kidnapping with the help of family members.  RELATED: Here's everything we know about King Jay Davila's death, arrests of his family members Christopher Davila, his mother, Beatrice Sampayo, 65; and his cousin, Angie Torres, 45, were arrested in connection with the baby's death. Christopher Davila is facing felony charges of injury to a child causing serious bodily injury - omission, child endangerment, tampering with evidence, felony possession of a firearm and possession with the intent to deliver a controlled substance. Sampayo and Torres are both facing a charge of tampering with evidence, which is a third-degree felony. Earlier this month, police Chief William McManus said charges could be upgraded and additional people may be arrested as the investigation continues. RELATED STORIES: Woman charged in baby King Jay's disappearance jumped by 3 inmates Memorial for baby King Jay Davila continues to grow SAPD: We 'believe that King Jay is deceased'; 3 charged in case, including father Nonprofits come together for memorial, burial service for baby King Jay SAPD locates 'potential witness' in case of missing baby King Jay after executing search warrant Woman gets involved in search for missing King Jay Davila SAPD: King Jay's kidnapping was staged by father to cover up foul play