Petechia on the lungs are more consistent with suffocation, particularly when petechia are also present on the mouth or pharyngeal tissues; finding these would tend to indicate the possibility of murder.
Pathologists look for a white foamy discharge in the airway as a confirmatory sign of drowning; generally they also look for water aspirated into the lungs, which is carefully examined for the presence of diatoms, which are tiny single-celled algae that are present in virtually all natural surface waters. Interestingly, the specific blend of diatoms can be used as a "fingerprint" to link the aspirated sample back to a certain body of water.
So overall, petechia and lack of foamy discharge and/or water in the lungs would point to a conclusion of dry suffocation. Finding water in the lungs that does not match the water the body is located in (for instance chlorinated drinking water in the lungs, body in a pond) would indicate that the body was drowned in one location and then moved to another.
Another consideration would be to see if the body has other external injuries consistent with struggling or being held under water.
I am attaching a link to an article about this that you may want to have a look at.