the source of that cash. officials say he traveled often to pakistan and spent five months there before returning to the u.s. in february. so where did he get the cash if he didn't have a job? big question. >> big question indeed. julie, thanks. >> federal investigators investigating the cause of the stock market plunge on thursday. the sudden drop leaving wall street stunned. one possibility being looked into was that a trader accidentally hit a wrong button triggering a massive selloff. that's possible? rick, i'm looking to you for the answer. the white house now throwing cold water on the idea that a typo sent wall street into a nose dive. >> two days after a 1,000 point drop in the dow, washington and wall street still don't have an explanation for exactly what happened. but an emerging theory is high speed computerized trades that are supposed to safeguard markets could actually be the culprit here.