Bitcoin Forum

This matter becomes more intriguing when taking into account how every Bitfinex transaction has to be co-signed by BitGo. If their service was not breached, it is unlikely their private key was issued to steal the funds. This leaves very few other options on the table, albeit one should exclude an inside job either at this stage.

http://themerkle.com/is-bitgo-to-blame-for-the-bitfinex-bitcoin-theft/