So: is Steve Rattner stepping down as the Obama administration's car czar because of the investigation into whether his private-equity fund used pay-to-play tactics to win business from New York's public pension fund?

Probably.

First, let's recap: New York Attorney General Andrew Cuomo has been conducting a broad investigation into whether investment funds paid politically connected middlemen to help them win contracts to manage state pension funds. Rattner allegedly arranged for the private-equity fund he co-founded, Quadrangle, to pay $1.1 million to the political consultant Hank Morris to help the fund win business from the New York pension board. Morris has since been indicted and charged with selling access to the board. The SEC is also conducting its own investigation.

Here's the evidence that suggests Rattner's unexpected departure is probe-related:

• The very day -- Monday -- that Rattner's departure was announced, both the New York Times and Reuters reported that Cuomo's probe of Rattner and Quadrangle had intensified. (Rattner is a former Times reporter and a close friend of publisher Arthur Sulzberger.) The following day, the AP reported that Cuomo is seeking a civil settlement with Rattner.

• In an email that Rattner sent to friends in February announcing that he was taking on the car czar job, he wrote that after 26 years on Wall Street, "I have begun a new phase of my life, in the public sector." As Slate's Mickey Kaus puts it: "Short phase."

• Rattner is a committed Democratic loyalist. He's a major fundraiser for the party, and his wife, Maureen White, is a former DNC finance chair. Given those ties, it's not hard to imagine that he could have been convinced to fall on his sword for the good of the president he helped elect -- a president who can ill-afford to see the man he put in charge of the auto bailout enmeshed in a Wall Street scandal.

• The Washington Post reports that some senior administration officials were taken by surprise by the abrupt announcement Monday of Rattner's resignation.

• Private equity expert Dan Primack, who has watched Rattner and Quadrangle closely, thinks there's a there there. Primack twittered Monday:

Steve Rattner just stepped down as auto czar. Know this: Rattner will be in the news again before end of summer, and it won't be about cars.

• Rattner -- who's not known to be media shy -- and Quadrangle have been notably mum since the resignation announcement.

Still, there's evidence on the other side:

• The major task that Rattner was hired to do for the government -- getting General Motors and Chrysler into and out of bankruptcy -- has been achieved, and far more smoothly than many expected. The Times reports: "A person who has worked with him in Washington said he understood that Mr. Rattner had decided to leave because his role on the task force had come to its natural end."

• Sources are saying that neither Rattner nor Quadrangle are likely to face criminal charges in relation to the pension fund probe.

So there you have it -- we report, you decide. But for ourselves, lets just say we're leaning in one direction on this one...

Late Update: One more point on the "yes" side of the ledger: The Treasury Department's statement on Rattner's departure said that he "has decided to transition back to private life and his family in New York City." That's pretty much the equivalent of saying he resigned to spend more time with his family. And we all know what that means.