The key to this case is the time interval between death and scanning - 9 hours is too long! Any inhaled gas that has been dissolved in blood/tissues under pressure (i.e. underwater) will have leached out into the blood at atmospheric pressure - a bit like what happens to a bottle of soda when the cap is removed! This is known as "off-gassing" and is a normal post SCUBA death phenomenon.
To make the diagnosis of gas embolism, there must be clear history of rapid ascent and rapid CT scanning (i.e. at least within 4 hours of death). The gas will be predominately in the left heart (it occurs due to rupture of alveolar sacs containing high pressure gas into pulmonary venules) and then into the systemic arterial circulation.
The other major differential diagnosis is putrefaction/decomposition. It occurs commonly and early in scuba death due to the presence of a wet suit (i.e. maintained body temperature). Gas is produced by bacteria in the bowel and enters the portal circulation thus gas in putrefaction is usually in the portal veins of the liver not the hepatic veins.