Nobody has been able to say just how the recession came to be, but researchers at the Federal Reserve Bank of New York say they have looked at data a new way, and they lay a good bit of blame on those who bought and flipped houses in the preceding years.

In their report, which they titled “'Flip This House': Investor Speculation and the Housing Bubble," the researchers say they "present new findings ... that uses unique data to suggest that real estate 'investors' —borrowers who use financial leverage in the form of mortgage credit to purchase multiple residential properties — played a previously unrecognized, but very important, role."

The researchers created charts based on how many first-lien mortgages property-owners held, and what they found stands out.

"At the peak of the boom in 2006, over a third of all U.S. home purchase lending was made to people who already owned at least one house," the report says. "In the four states with the most pronounced housing cycles, the investor share was ... 45 percent. "