Allegedly they were hacking into news services and reading news before it was publicly released, which means their investing time frame was measured in hours and minutes.
This makes it much easier for the SEC to find this type of behavior as these types of trades, especially in the options markets stand out, when done at large sizes.
The SEC takes alot of grief, some well earned, but you should assume that when a stock moves, they'll run an automated scan of every trade that profited from that in the days/hours leading up to that move and over time they'll cross reference those trades to watch for accounts that continue to do this over time when they have reason to suspect illegal activity.
Think of it like athletes blood samples being held for years after competition. They won't test all the samples held but they have the data there to look back on if they find a reason to.