NEW YORK (Reuters) - A $10,000 reward offered by the "Doonesbury" comic strip for proof that President Bush served in the Alabama National Guard during the Vietnam War has elicited over 1,300 responses but turned up no credible evidence yet, the cartoonist said on Friday.

With so much controversy surrounding Bush's National Guard service, a credible witness would have turned up by now if there was one, said Garry Trudeau.

Earlier this week, a spokeswoman for the Republican National Committee denounced the contest as a "silly stunt." Trudeau agreed.

"She's right," he said. "But as a simple investigative cartoonist, I don't have a very big tool kit."