It was in fact, Len Sassaman.

From anonymous remailers and his penchant for anonymously released work back in the mailing lists, to MojoNetwork with Bram. His British spelling, his time zone abroad when working in academia and posting online. His circle. Before he committed suicide due to his neurological issues and loss of passion for life, Satoshi last said

“I’ve moved on to other things and probably won’t be around in the future.”

He kept this secret even from his own wife. Alas, I hate to post this here just like this but it's my belief that it's an open secret. Only those close enough to suspect and know his pathology venture the guess. His wish is to have the work carried on nameless and to speak for itself. He hated notoriety for notoriety sake. I feel disrespectful even posting this, but it was not fucking Nick Szabo.

The most likely explanation I've read is that Szabo was involved on the Bitcoin project, at the behest of US Intelligence (perhaps team lead, working within a defined set of goals - it's speculation for now). Bitcoin is a very effective means of destabilizing currencies and extracting wealth out of non-friendly areas, so for the US Intelligence community it is a boon.

Szabo later went on to improve on the concept with Monero, without the involvement of US Intelligence (obviously, since Monero is very unfriendly for the US Govt). Again, speculation. The only person capable of creating both, is likely Szabo. Monero being a big middle finger to "the team" behind Bitcoin, who still control the keys.

I am glad Obama gave Nick SS protection.