The ex-deputy, Paul Schene, was charged with fourth-degree assault in the videotaped beating of 15-year-old Malika Calhoun on Nov. 29, 2008.
But after two days of deliberating - and days of hearing testimony and watching a videotape of the incident - jurors said they were unable to agree on whether the deputy is guilty or innocent.
On Friday, a mistrial was declared after jurors reported to the judge that they were a "hung jury."
Senior Deputy Prosecutor Gary Ernsdorff said the case would be retried.
"We will be showing the video and the rest of the evidence in another King County courtoom in the near future," he said, adding he believes the prosecution had a strong case and he doesn't see the need to change anything when they retry it in the future.
Defense attorney Peter Offenbecher said he was disappointed he couldn't persuade all 12 jurors that Schene’s conduct was lawful. "And if the case is tried again, we’re hopeful we will be able to persuade all 12 of the jurors that it was lawful," he said.
Jurors exiting the courtroom refused to explain why they couldn’t agree on a verdict or what the vote count was.
"The one thing the jury agreed on was that they didn't want to talk to anybody," said King County Prosecutor Dan Satterberg. "They may change over the next couple of days, they may call in - sometimes they'll want to give comments later. But they didn't really want to be interviewed by anybody, and they've left the courthouse."
Surveillance footage showed the deputy manhandling the teenage girl, throwing her down on the floor and beating her in a holding cell at SeaTac City Hall.
"During the attack, Malika was so scared she wet her pants," Ernsdorff said during the trial.
Prosecutors added Calhoun's friend in a nearby cell heard the girl screaming, "I am not resisting!"
Satterberg said the jury came to the judge on Thursday, during deliberations, to report that one juror was so incensed over what she saw on videotape of the incident that it was affecting her ability to be impartial.
"There was a statement by one of the jurors who has a daughter about the age of the victim in the case, and she made a statement very strongly that she thought what happened was outrageous and that she couldn't be fair," Satterberg said.
But he said the issue was resolved between the judge and jury.
"There's a lot of times when we have difficult cases where jurors are disturbed by what they see. I think they resolved that pretty easily, and she said she could be fair, and she could go on," Satterberg said.
Defense attorney Peter Offenbecher says Schene didn't do anything wrong. He said his client, having been hit by the girl's shoe, was trying to bring the girl under control using a safe take-down method.
"He did exactly what he was trained to do under these circumstances. It does not constitute a crime of assault or any other crime," said Offenbecher.
Schene also took the witness stand in his own defense during the trial to say his use of force was justified.
Under questioning from his attorney, Schene said he was following his training when Malika Calhoun kicked a shoe at him, striking him in the leg.
The tape shows Schene rush into the cell, kick the girl, then push her against a wall before throwing her to the ground, where he punched her.
Schene testified that he used lawful techniques to subdue her.
"It was to stop her from assaulting me again, place her in handcuffs, restrain her and put her back on the bench," he said. "This is trained. This is trained in the academy."
Calhoun and her friend had been taken into custody for investigation of auto theft. In the minutes leading up to the scuffle, Calhoun was confrontational, prosecutors said, but Schene egged her on, implying she was a prostitute.
But Offenbecher said it was natural for Schene to ask whether the girls were prostitutes, since they were arrested in a high-prostitution area in the middle of the night.
Calhoun, an African-American, said Schene used a racial slur in addressing her. But prosecutors decided there wasn't enough evidence to pursue the case as a hate crime.
The sheriff fired Schene last September for a number of policy violations, including the video-taped incident.
Schene stood next to his attorney in the hallway after the mistrial was declared, but refused to answer questions from reporters.