Such petechiae are present in nearly 90 percent of SIDS victims. They are far less common in infants or children dying of external suffocation. At this moment, the respiratory muscles are in a position to generate strong efforts to breathe in, which can generate high suction pressures in the chest cavity. Strangulation, or external suffocation, will occur at random points in the respiratory cycle, only occasionally happening at the instant when we suspect the obstruction of SIDS may occur. In conclusion, I do not know the cause of SIDS, though I believe the mechanism may be a sudden internal obstruction of the upper airway during sleep.
Nobody knows for sure.
A concept that I have found appealing for many years is that this stoppage, or obstruction, of the airway is not due to a disease process or abnormality of the baby, but is a reflection of the fact that babies at this time of life are undergoing an incredibly rapid state of growth and maturation. Many important changes are occurring at the age when most SIDS occur. The infant is, among other things, coming into an age where he is beginning to sleep through the night. That's not just a simple change in habit pattern, but a change that is very fundamental and has to do with control mechanisms in the brain. Centers that are beginning to be active in the baby's brain didn't even exist when that infant was born.