James R. Burritt who worked for Thomas H Lee also assisted Jeffery Epstein's Liquid Funding which took commercial mortgages and investment-grade residential mortgages bundled into complex securities.
A lender would give a borrower cash in exchange for securities that the borrower will buy back at an agreed upon date for a fixed price, usually at the 1st of the next month. It was a way to shift debts off the ledger temporarily to get a high rating but then buy them back again.