I guess that this is a case of the fan hitting the sh1t.

Gilroy police Sgt. Kurt Svardal said authorities have no idea where the plane was from or where it was going. The aircraft came pretty much straight down into a holding tank filled with raw sewage at a sewage treatment facility. It was too dangerous for even a dive team to go into the water and check for bodies or the tail number of the plane, which would indicate who owned it and where it was from.

The tank is about 20 feet deep and will have to be drained before police can determine if anyone is inside.

Don't sign me up for that accident investigation. Reportedly, a very large number of last words from pilots on voice recorders is "Sh!t!" There's no voice recorder on this plane, but I wouldn't be surprised if the pilot used that word, in this case literally.

About the only ways a plane would come down "pretty much straight down" are:

a) some form of structural failure, such as the loss of the horizontal stabilizer(s) or (more unlikely) the wings, or

b) a deliberate dive.

Even if it was a deliberate dive, the plane would be trying to pull out. Positive stability would cause the plane to try to recover from a dive unless it was horribly out of trim or severely damaged.

If it was a deliberate dive, I hope it was a terrorist who thought he was damaging some vital infrastructure. Dieing in a big vat of sh1t is a fitting end for such a person.