Ken said his sister was there, and Ken said his sister said an agent said...
Or, maybe not quite.
"Agents entered the casino around 7 a.m. and proceeded to tell guests to stop playing and keep their hands away from the tables, said a casino restaurant employee to KTLA."
https://www.pokernews.com/news/2017/04/feds-shut-down-bicycle-casino-for-criminal-fraud-27555.htm
"Blackjack and gambling tables were shut down and early-morning gamblers were told to cash out."
http://losangeles.cbslocal.com/2017/04/04/feds-raid-bicycle-casino-in-criminal-fraud-investigation/
My guess is the reason there were so many agencies invovled -
HSI, IRS, Cali DoJ, US Attorney's office - was just to have enough manpower to shut down and secure the whole place at once. Tables, cage, back rooms - there's a lot to cover.
If the laundering involved what was going on specifically at the tables at the time of the hit, they'd want to freeze the games with the chips in front of the players (as on camera), with the cash in those drop boxes (possibly marked/tracked), etc. If the laundering activity were going on at 7am on Tuesday, it's probably being done then specifically to isolate it from other gambling, so that the money launderer's take can be easily tracked for the illicit business books.
On the other hand, maybe they just wanted the records and back-room stuff, and so they hit the joint at 7am on Tuesday to minimize player impact, and it had nothing to do with the current action on the tables.
Either way, all the reports seem to indicate the casino will be back in business tomorrow - so staff may not be invovled, or if some are, then it's just a subset. It's possible that Mgmt. was cooperating with the authorities - that helps explain why they knew to pick Tuesday at 7am, pretty much the slowest point in a casino's week.