Edward Nero, one of the six officers charged in the arrest and death of Freddie Gray, alerted supervisors in January while working with the Foxtrot helicopter unit that he had observed Baltimore County police officers kicking and punching a suspect, according to a police report.
One of the officers is now facing criminal assault charges.
Nero was the first officer charged in the Gray case to be acquitted, following a bench trial in May 2016. He had faced misdemeanor charges of second-degree assault, reckless endangerment and two counts of misconduct in office for his role in Gray's initial arrest.
Administrative proceedings for the officers, who were all acquitted or had their cases dropped by prosecutors, remain pending. The officers have been serving in administrative roles, with Nero working with the helicopter unit.
According to a report Nero filed with supervisors Jan. 25, he was flying with two other officers to assist officers who had pursued a stolen vehicle into Baltimore County.
"While placing the suspect under arrest, one officer appeared to kick the subject in the head area and then kick the suspect two more times," Nero wrote. "Another officer appeared to punch the suspect as well."
Officer Christopher Spivey was charged two weeks later with second-degree assault, with authorities saying they were notified by the Baltimore police internal affairs unit that a "crew member" of the aviation unit had witnessed a possible assault.
No other officers have been charged.
Spivey's defense attorney, Brian Thompson, said the officer "acted lawfully and in accordance with his training."
"We are confident that a Baltimore County jury will agree once they have been presented with all of the evidence in this case," Thompson said.
Michael Davey, an attorney for the police union, declined to comment on Nero's behalf. "On that day, he was simply doing his job," Davey said.
Nero's report regarding the alleged assault said he was in a police helicopter with an Officer Bilheimer. Bilheimer was called as a prosecution witness during the trial of Officer William Porter because Bilheimer was a training academy instructor when Porter was taught how to handle injured detainees.