The reason they're faking the mortgage documentation? If the bankers admit what's wrong with the chain of title conveyance, the mortgage loans are no longer eligible for the trusts the bankers sold to investors -- and under their own terms of agreement, the chain of title was breached, "true sale" was probably not achieved and the liability reverts to the banks.

Investors are likely to sue to recover their money. The government will probably stand behind Fannie Mae and Freddie Mac investors, but private banks are another matter. Some major dominoes seem likely to fall.

It's important that we don't fall for the media misdirection here: It's not "poor banks getting screwed by mortgage deadbeats." It's really "poor investors getting screwed by banks who knowingly sold them worthless mortgage bonds." Felix Salmon:

This kind of information was valuable to Citigroup: it showed them that the quality of the loan pool was much lower than you’d think just by looking at the ostensible underwriting standards.

Armed with this information, Citigroup would do two things. First of all, it would take those 582 rejects and put most of them back to the underwriter. Essentially, they said, the loans weren’t as advertised, and they didn’t want them. But Citi would still keep some of them in the pool.

But remember that Clayton had tested only a small portion of the loans in the pool. So Citi knew that if there were a bunch of bad loans among the loans that Clayton tested, there were bound to be even more bad loans among the loans that Clayton had not tested. And those loans it couldn’t put back to the originator, because Citi didn’t know exactly which loans they were.

If there had been any common sense in the investment banks, that would have been the end of the deal. But there wasn’t. Rather than simply telling the originator that its loan pool wasn’t good enough, the investment banks would instead renegotiate the amount of money they were paying for the pool.

This is where things get positively evil. The investment banks didn’t mind buying up loans they knew were bad, because they considered themselves to be in the moving business rather than the storage business. They weren’t going to hold on to the loans: they were just going to package them up and sell them on to some buy-side sucker.

In fact, the banks had an incentive to buy loans they knew were bad. Because when the loans proved to be bad, the banks could go back to the originator and get a discount on the amount of money they were paying for the pool. And the less money they paid for the pool, the more profit they could make when they turned it into mortgage bonds and sold it off to investors.

Now here’s the scandal: the investors were never informed of the results of Clayton’s test. The investment banks were perfectly happy to ask for a discount on the loans when they found out how badly-underwritten the loan pool was. But they didn’t pass that discount on to investors, who were kept in the dark about that fact.

I talked to one underwriting bank — not Citi — which claimed that investors were told that the due diligence had been done: on page 48 of the prospectus, there’s language about how the underwriter had done an “underwriting guideline review”, although there’s nothing specifically about hiring a company to re-underwrite a large chunk of the loans in the pool, and report back on whether they met the originator’s standards.

In any case, it’s clear that the banks had price-sensitive information on the quality of the loan pool which they failed to pass on to investors in that pool. That’s a lie of omission, and if I was one of the investors in one of these pools, I’d be inclined to sue for my money back. Prosecutors, too, are reportedly looking at these deals, and I can’t imagine they’ll like what they find.

The bank I talked to didn’t even attempt to excuse its behavior. It just said that Clayton’s taste-testing was being done by the bank — the buyer of the loan portfolio — rather than being done on behalf of bond investors. Well, yes. That’s the whole problem. The bank was essentially trading on inside information about the loan pool: buying it low (negotiating for a discount from the originator) and then selling it high to people who didn’t have that crucial information.

This whole scandal has nothing to do with the foreclosure mess, but it certainly complicates matters. It’s going to be a very long time, I think, before the banking system is going to be free and clear of the nightmare it created during the boom.