WASHINGTON (AP) – Roger Clemens will have to wait until September to find out if he’ll start a new trial on charges of lying to Congress about using performance-enhancing drugs.

On the second day of testimony today, a judge in Washington declared a mistrial — after prosecutors showed evidence to the jury that the judge had said they couldn’t show. The judge said the former pitching star couldn’t receive a fair trial after that.

Clemens and his lawyers are still under a court gag order, and they didn’t comment as they left the courthouse. Clemens signed autographs and a couple of baseballs for fans.

The issue that caused the mistrial involved testimony from Clemens’ former teammate and close friend Andy Pettitte, who says Clemens told him in 1999 or 2000 that he used human growth hormone. Pettitte also says he told his wife, Laura, about the conversation the day it happened. Prosecutors had wanted to call Laura Pettitte to back up the account, but the judge had said he wasn’t inclined to allow it. But in a video that prosecutors showed to jurors, a congressman referred to Pettitte’s conversation with his wife.

The judge said prosecutors had made a grave mistake. Prosecutors said he could just tell the jury to disregard what they saw — but the judge said he couldn’t “un-ring the bell.”