But prosecutors argued that her head trauma must have been caused by shaken baby syndrome, a diagnosis popularised in the late 1990s as evidence of physical abuse in infants and toddlers. But that diagnosis has been increasingly rejected, as doctors and medical researchers point out that the symptoms of shaken baby syndrome namely, bleeding or swelling in the eyes or brain can be caused by other conditions. Roberson's defence team has argued that Nikki suffered from chronic pneumonia in the lead-up to her death, and the medications she was given, including codeine, contributed to her death.