The officer's supervisor in the police station lockup is also liable for not stopping the misconduct, according to U.S. District Judge Matthew F. Kennelly.
The judge issued the ruling Monday in a civil case concerning the treatment in custody of Philip Coleman, who died at a hospital hours after the incident in the cell
in December 2012.
Coleman, 38, was found to have died from an adverse reaction to an antipsychotic drug administered at the hospital.
But his father, Percy, has sued the City of Chicago and some police officers, alleging their repeated use of excessive force was responsible for his death.
Judge: Officer 'chose to use brute force'
The case has received fresh attention amid public criticism and protests
over police practices in Chicago.
Last week, the city released videos that showed officers using a Taser on Philip Coleman in the cell and then hauling him out along the ground.
"I do not see how the manner in which Mr. Coleman was physically treated could possibly be acceptable," said Chicago Mayor Rahm Emanuel, who is grappling with the crisis surrounding the city's police departmen
Judge Kennelly gave a similar view in his decision Monday, which focused specifically on the dragging of Philip Coleman along the ground.
Officer Keith Kirkland, who pulled Philip Coleman out of the cell, "chose to use brute force when it was no longer necessary," the judge said.
And Kirkland's supervisor, Sgt. Tommy Walker, "could have ordered Officer Kirkland not to drag, or to stop dragging Mr. Coleman" but chose not to do so, Kennelly said.
Damages against the two defendants will be determined by a jury at trial, according to the ruling.
Father: 'I hope they'll lose some sleep'
The judge's decision Monday was in response for a request for summary judgment on the dragging incident by Percy Coleman, the administrator of his son's estate.
It doesn't cover the use of the Taser in the cell or the later use of force against Philip Coleman at the hospital.
"I bet the officers thought they'd go home free until today's ruling," Percy Coleman said in a statement Monday provided by his attorney. "Now, I hope they'll lose some sleep just like we've lost sleep, as yesterday was the three-year anniversary of our son's death."
CNN wasn't immediately able to reach Kirkland, Walker or their representatives for comment late Monday.
The Chicago Tribune reported
that Kirkland is a civilian detention aide and that Walker is now retired.
Mayor Emanuel, who has replaced top police officials in recent weeks, has said he doesn't consider the investigation into what happened to Philip Coleman to be over.