Mr. Feygin now regards the letter as a forgery. “It was all subterfuge,” he said, in comments reported by the newspaper Ukrainska Pravda, “and it didn’t take place without the participation of special services of the Russian Federation.”

Ms. Savchenko’s refusal to drink water had gone on for five days, through the closing arguments in her trial and her defiant final statement to the court, and she had vowed to carry on. Ms. Savchenko, a 34-year-old veteran of a Ukrainian deployment to Iraq before her more recent duties in Ukraine, was detained under unclear circumstances and is on trial in Russia for the murder of two journalists.

The Russian authorities accuse her of acting as an artillery spotter and directing mortar fire at a rebel checkpoint where the television reporters were filming. Ms. Savchenko denies this. Her backers say she was captured before the mortar strike and illegally bundled across the border to Russia to stand trial. Since then, Vice President Joseph R. Biden Jr. and Chancellor Angela Merkel of Germany, among others, have called for her release.

In Kiev, the Ukrainian capital, she has become a cause célèbre, and about 2,000 people rallied in her support on Sunday. For her final statement on Wednesday, she stood on the defendants’ bench, made the lewd gesture, sang the national anthem and called the process “the farce of Kremlin puppets.”

In her comments, Ms. Savchenko dared the judge to impose the 23-year sentence prosecutors have requested. “If you want to show your strength, go ahead,” she said. “But remember, we are playing with my life. The stakes are high, and I have nothing to lose.”