NewsChannel 5's cameras were there last month as Casada woke up last month to an FBI raid on his Franklin condo.
Now, Casada has told associates that the FBI had questions about how he helped pass Lee's legislation to create school vouchers to pay for private school tuition. Two independent sources, who spoke on the condition that they not be identified, said Casada described being questioned about allegations of bribes being offered for votes.
The Williamson County Republican has denied offering bribes to anyone.
"One of the reasons that the search warrant is typically the first overt item of an investigation is so that there’s an element of surprise," Purser told NewsChannel 5 Investigates.
Casada's criminal defense attorney, Ed Yarbrough, declined to comment on what agents asked his client.
In April 2019, when Casada was still speaker, a House vote on Lee's voucher bill failed on a 49-49 tie vote.
But Casada kept the vote open while he searched for a 50th vote.
Livingston Democrat John Mark Windle first told NewsChannel 5 Investigates that Casada dangled the prospect of a lucrative National Guard promotion -- from colonel to general -- in exchange for his vote.
Windle said he rejected the offer, insisting his vote was "not for sale."
Lee, who has the authority to make National Guard promotions, has insisted he knew nothing about the offer.
This revelation follows weeks of speculation that the investigation's focus appeared to be centered on alleged efforts by Casada and his associates to steer anonymous money into political campaigns.
Purser said it could be about both.
"Once the search warrant is under way, there is no limit on the topics that can or should be discussed, no," the veteran agent explained.
In fact, House members had described a wheeling-and-dealing atmosphere that led to Casada eventually getting his 50th vote.
Among those involved: Casada's then-chief of staff, Cade Cothren, whose home was also among those raided.
"Cade Cothren comes to me on the House floor and says that 'we' - meaning he and the Speaker- need my vote on vouchers and what would I like?" Hawk told NewsChannel 5 Investigates back in 2019.
His response?
"To Cade Cothren, I said, 'you and the Speaker of the House have nothing that I want.'"
Casada has described allegations of possible bribes as being "ridiculous."
But just days after the vouchers bill passed the House, NewsChannel 5 has learned, FBI agents showed up at the home of one state representative.
That lawmaker, who asked not to be identified, said agents wanted to know about campaign contributions being offered to support the reelection efforts of those willing to vote for the bill.
"The availability of phones and computers, anything electronic like that, that could very well be a critical component of the investigation," he suggested.
Purser said that, with the FBI seizing the cell phone of one Casada associate, along with computers and all sorts of other files, investigators will have a significant trail to follow in the days and weeks ahead.