It looks like social networking site ConnectU‘s lawsuit against Facebook may not be over yet. Although the two companies agreed to settle in April (and have since signed the paperwork) ConnectU attorney John Hornick told a judge yesterday that his clients want to pull out of the deal, according to Bloomberg News.

Since reaching the agreement, Hornick said ConnectU has found instant messages on Facebook’s computers that are a “smoking gun” backing the company’s allegations. U.S. District Judge James Ware still needs to approve the deal, and Hornick said that if they’re “forced into a settlement,” ConnectU’s founders will file a fraud claim.

Judge Douglas Woodcock didn’t have much sympathy for Hornick’s argument, characterizing it as “buyer’s remorse.”

Back in 2003, when they were all at Harvard, Facebook founder Mark Zuckerberg worked for ConnectU’s co-founders Cameron and Tyler Winklevoss, helping them develop a campus dating site called Harvard Connect. After Facebook took off, the Winklevoss brothers filed suit against Zuckerberg and his startup; they alleged he stalled their project while stealing ideas and code for himself. The case has revealed some embarrassing details about Zuckerberg, including his diary, and could also be liability if Facebook wants to make a public offering. The details of the settlement are secret, but it will definitely be a step backward of Facebook can’t put this legal battle behind it.

I emailed Facebook, but a spokesperson declined to comment on the case.

I won’t waste your time weighing in on whether this makes Facebook look more or less guilty, because your guess is as good as mine. But I will reiterate Woodcock’s point that it looks silly and embarrassing to reach a settlement while you’re still going through the evidence, and then try to call the whole thing off when (surprise!) you find new information in that evidence. The Winklevoss brothers may agree, and are apparently unhappy with the legal advice that led to the settlement — CNET reports that they’ve hired a new attorney.