Mercedes Casanellas and her British husband, Richard Cushworth, went home with a baby whom they weren't quite sure was theirs. When the baby's skin color darkened, that tipped them off.

After a DNA test confirmed their suspicions, they made a plea to the hospital staff and others to help find their child.

The Salvadoran Attorney General's Office asked four mothers whose babies were born at that hospital on the same day to bring their infants in for DNA testing.

One test matched Casanellas and Cushworth.

The couple claims that the doctor purposely switched out their baby as part of a child-trafficking ring. Both the doctor and the hospital deny the charge. Authorities are now investigating the doctor.

This video includes images from Getty Images.