The former Los Angeles Laker and his daughter Gianna died Sunday in the crash, and as many as seven other people may have been killed.
The man was taken into custody by Prince George's County police responding to reports that a driver had struck multiple vehicles.
The new research looked at cancer patients who took part in a study nearly five years ago.
"It was obviously very sad and he had bad motives, but the way he was able to lead was second-to-none," the coach said.
Both Tristen Watson and her 17-month-old child died of gunshot wounds to the head in a suicide and homicide, the coroner's office said.