WHITE PLAINS — A federal judge yesterday tossed out the conviction of a former jail guard, acquitting him of violating the civil rights of an inmate who died after he was kicked into a coma.

The unusual action drew criticism from a federal prosecutor.

A jury in September deliberated four hours before convicting Paul Cote in the attack on Zoran Teodorovic, a mentally ill homeless man who died 14 months after the October 2000 beating.

U.S. District Judge Charles L. Brieant said in a written opinion yesterday that he found the verdict reached after a week-long trial “deeply troubling.” He said he was not satisfied that “competent, satisfactory, and sufficient” evidence supported the jury’s finding.

He also said he had “real concern that an innocent person may have been convicted” because much of the testimony defied physical realities portrayed in photographs during the trial.

In a statement, U.S. Attorney Michael J. Garcia said: “We are very disappointed in Judge Brieant’s decision overturning the jury’s verdict and are thoroughly exploring our appellate options.”

At trial, the government had argued that the altercation began when Teodorovic punched another correction officer at the Westchester County Jail in Valhalla and the officer, Mark Reimer, wrestled him to the floor.

Prosecutors said Mr. Cote rushed over and pummeled Teodorovic.

Mr. Reimer, who agreed to testify in exchange for immunity, said he had tried to stop Mr. Cote’s attack, which included punching, kicking, and stomping.

Mr. Cote’s lawyer told the jury that Mr. Reimer did not have control of the inmate, who was in jail for criminal trespass, when Mr. Cote arrived and Mr. Cote “did not use excessive force.”