Cayman Islands Magistrate Valdis Foldats dismissed the case against Magistrate Khamisi Tokunbo, who denied a charge of refusing to take a breath test.
Mr Tokunbo, 65, was arrested at the scene of an accident in January.
In the ruling handed down on Monday, the Magistrate ruled that the arrest was illegal and dismissed the charge.
He also found that Colin Mill, the arresting officer, had shown bias against Mr Tokunbo which tainted the police investigation.
“As a witness, Pc Mill was unresponsive, evasive, self-contradictory and disingenuous,” he said.
“His bias against the defendant tainted his actions at the scene and his testimony before this court.”
Police were called to the crash, near the public entrance to Elbow Beach, where they found Mr Tokunbo’s car “completely off the road” – over an embankment.
Both Mr Tokunbo and his friend, Allen Robinson, were in the vehicle at the time. Mr Tokunbo denied that he was driving the vehicle when the accident occurred.
His lawyer, Charles Richardson said: “It was the right decision.”
In a post published on Facebook after the ruling, he wrote: “A passenger, not in control of a vehicle, is not obliged to cooperate with a demand for a breath test.
“Such a demand by a police officer would be unlawful, and in those circumstances, no offence would lie, if that passenger refused that request.
“Further, there were no direct witnesses to the accident at the material time, they arrived after the incident had occurred.”
Mr Richardson added that his client “did not deny he had consumed a few”.
“But he maintained he was not the driver, and with no direct witness to contradict him, remember, unless it was proven he had control of the car at the crucial time, no offence can lie against a passenger who may be intoxicated, and similarly that passenger is under no obligation to comply with a demand for a breath test.
“It was the right decision.”
Lawyer Mark Diel appeared for the Crown.
The written reasons for the Magistrates’ ruling will be released in due course.