Sources: Federal agents seize documentation, cash from Ron & Mike's Football Pool

— -- One of the largest football survivor pools was shut down this week after federal agents seized documentation and the money the pool organizers collected, sources told ESPN.

Several participants in Ron & Mike's Football Pool said there were at least five NFL survivor pools this season with at least $2.5 million at stake to the winners. The participants spoke under the condition of anonymity and had access to the website from the beginning of the season.

"Please be advised that the Ron and Mike website has been forced to shut down at this time and is unlikely to open again," read a note sent to people who were still alive in the pools.

"We understand your frustration and anger at this time but closure of the pool is beyond our control. We apologize to those that are still alive in our various pools and we ask for your patience and understanding while we contemplate the next steps. Unfortunately at this time we cannot make any additional comments."

Sources said the organizers, who were running the pool for at least the past eight years, are Ron Kronengold and Mike Bernstein. Joe Conway, the attorney representing the men, confirmed that the website was voluntarily shut down after circumstances earlier in the week caused their business to be compromised. Conway said that neither he nor his clients have been furnished with any information from the government, other than a search warrant.

If Kronengold and Bernstein merely ran the pools and took no share of the winnings, it would not be illegal, per New York state law. However, if they did receive a cut of the winnings, which is usually 10 percent, they could be charged with bookmaking and profiting from a gambling activity. The rules and conditions to entries did not include any quid pro quo to give the organizers a cut.

ESPN has learned that the warrant to seize records and money was issued by federal prosecutors in the Eastern District of New York. Officials there declined to comment, citing office policy against confirming or denying the existence of an investigation.

ESPN has learned that two pools, blue and red, were each capped at close to 10,000 entries with a cost of $100 per entry. Those filled up so quickly that a second-chance pool was created, sources said, at $200 apiece. A high-roller survivor pool was also offered at $500 per entry. Another pool, which started midway through the season, was a second-half pool and cost $100 per entry.

All the pools combined had more than 23,000 entries, players with knowledge of the contests said, with a collective value that surpassed $2.5 million.

Survivor pools require a bettor to pick one team that is going to win each week of the football season without using the same team twice. Once a team that is picked loses, that person is eliminated. In Ron & Mike's Football Pool, those still remaining had to pick two teams to win in Weeks 11 through 15 and three teams in Weeks 16 and 17 in order to produce a winner from so many entries.

The organizers did plenty to conceal the operation. Money to the pools, all in cash, was asked to be addressed to Green River in Plainview, New York. A mortgage brokerage called Green River Capital is in Plainview, but neither man works there. The mailing address provided corresponds to a box inside a UPS store.

The two weren't completely covert about their operation. Kronengold filed to trademark the name "Ron & Mike's" for survival pools in 2011. He received the trademark in 2012.

The shutdown is the biggest pool bust since 2010, when prosecutors in New Jersey arrested a school teacher named John Bovery for running a $100 per entry survivor pool that had roughly 8,000 entries and charged him with promoting gambling and money laundering. After 5? years, the case still had not gone to trial, so Bovery was put into the pretrial intervention program.

The state still has the $846,000 it seized from Bovery's bank accounts, $123,000 of which he maintains were his life savings unrelated to the pool.

ABC News correspondent Aaron Katersky contributed to this story.