I linked above (a week ago -ish) to a study showing that fingerprints can be retrieved from metal surfaces up to 70 days after immersion. In, the same post or just above it I mentioned that the orientation of the fingerprints on the blade could be used to determine how the blade was used (ie. cutting v's scraping a surface, amount of pressure etc).
I admit that seven days in water will make a lot of trace disappear and perhaps the small wounds on the fingers can not be microscopically matched to the specific blade found in the pocket and perhaps there are no fingerprints...but the police/ME must have something other than their theory to determine "self-inflicted". I really do not believe they would have used that term without reason, unless of course, they we really, really trying to avoid the press drawing their own conclusions about the nature of the cuts and the possibility of them being "self-defense injuries". And why would they do that unless they had a reason to know that they were not self-defense wounds and that yes, this was a suicide...
ETA: Still on the fence (with good company though) and just playing devil's advocate above.