Britney Spears' former business managers have some deep, dark secrets they don't want the public to know about ... at least that's how her attorney interprets their radio silence.
Mathew Rosengart fired off a letter to Tri Star Sports & Entertainment Group earlier this week ... repeating his demand for them to turn over a bunch of documents. Specifically, he's investigating exactly how Lou Taylor's company ran Britney's life ... financially and otherwise.
In the letter TMZ obtained in a court filing, Rosengart says one thing he's demanded -- but not received -- for more than 6 weeks is the total amount of fees Tri Star's taken from Britney since 2008. He says, "Tri Star's ongoing failure to answer this question speaks volumes and leads to the unfortunate and inexorable conclusion that Tri Star has much to hide."
Some sources intimately familiar with her finances tell TMZ ... they believe Britney's net worth -- estimated at $60 million -- should be 2 to 3 times more than that, and they attribute that shortfall to misappropriation by people associated with the conservatorship.
Rosengart's concern goes beyond money, though. He's also keyed in on the allegation Tri Star had a hand in spying on Britney by placing listening devices in her bedroom ... as reported in the most recent NY Times documentary about Brit and the conservatorship.
He claims that reporting is more than enough to warrant Britney's desire to comb through any and all Tri Star docs related to the alleged electronic surveillance.
As we reported, Taylor's company has filed its response to Rosengart ... which includes a flat out denial from Robin Greenhill, Taylor's right-hand woman, that Tri Star had anything to do with bugging Britney.