COLUMBUS, Ohio (WKRC/CNN Newsource) - An Ohio coroner has released a cause of death for the baby who was kidnapped, along with his twin brother, in December.

Ky'Air and Kason Thomas, who were five months old at the time, were abducted in a car in Columbus on Dec. 19.

Police say 24-year-old Nalah Jackson stole the car outside of a restaurant while the babies' mother briefly went inside to pick up an order.

After a few hours, Ky'Air was found outside of the Dayton International Airport, still in his baby seat.

Two days later, Kason was found near a pizza restaurant in Indianapolis. Both boys were safe and reunited with their family.

Indianapolis Metro Police located Jackson that day and took her into custody. She's charged with two counts of kidnapping a minor.

On Jan. 28, emergency units were called to the twins' family's home for a medical emergency.

Ky'Air was found not breathing. He was rushed to the hospital, where he died overnight.

An autopsy was performed, and a death investigation was launched. The cause of death has now been ruled sudden unexplained infant death (SUID).

The report says Ky'Air was placed face-down on an adult bed with excess bedding and pillows, and left unsupervised.

No signs of trauma, foul play, abuse, or neglect were found, according to the coroner's office.