MEMPHIS, Tenn. — A former Memphis police officer testified Thursday at the federal trial of three ex-officers facing charges related to the January 2023 beating death of Tyre Nichols that he believes he panicked during the encounter.

“I lost my composure,” Desmond Mills Jr., who pleaded guilty to charges connected to the beating death of Nichols, said when he was asked about accidentally pepper-spraying himself during the encounter, according to WATN, the ABC affiliate in Memphis covering the case in the courtroom. “I felt like I was panicking.”

Justin Smith, Demetrius Haley and Tadarrius Bean were charged on Sept. 12, 2023, with violating Nichols' civil rights through excessive use of force, unlawful assault, failing to intervene in the assault and failing to render medical aid. These charges carry a maximum penalty of life in prison, according to the U.S. Department of Justice. The officers have pleaded not guilty to all charges.

Mills and Emmitt Martin III, the two other officers who were also charged in this case, have pleaded guilty to some of the federal charges.

Mills pleaded guilty to two of the four counts in the indictment -- excessive force and failing to intervene, as well as conspiring to cover up his use of unlawful force, according to the DOJ. The government said it will recommend a maximum penalty of 15 years in prison, based on the terms of Mills' plea agreement.

Martin pleaded guilty to excessive force and failure to intervene, as well as conspiracy to witness tamper, according to court records. The other two charges will be dropped at sentencing, which has been scheduled for Dec. 5, according to the court records.

On Wednesday, Mills reiterated his testimony from the day before that he was angry he sprayed himself with pepper spray, and therefore used excessive force on Nichols, according to WATN.

“I was angry because I just [pepper] sprayed myself in the face,” Mills said on Tuesday, according to WATN. “I didn’t give him a chance to give me his hands.”

Judge Mark Norris told the jury on Wednesday to disregard the emotional part of Mills' Tuesday testimony, when Mills was asked who used excessive force in the police body camera footage from the night of Nichols' beating, according to WATN. Mills did not answer the direct question, instead breaking down in tears on the stand.

“I wish I would’ve stopped the punches. It hurts to watch. It hurts inside so much," said Mills, who cried during his testimony, according to WATN. "It felt bad every time the picture is on the screen to know I’m a part of that. I made his child fatherless. I’m sorry. I’m sorry. I know 'sorry' won’t bring him back, but I pray his child has everything he needs growing up."

"We're praying for everyone involved," Ben Crump, the civil rights attorney representing the Nichols' family, said during a prayer vigil Wednesday morning outside the courthouse when asked for his response regarding Mills' emotional testimony.

Crump said this trial was one of the most emotional trials he has ever attended, a sentiment shared by Antonio Romanucci, his co-counsel.

"In my career, which is now over 40 years," Romanucci said, "I have never seen such testimony as I did yesterday -- police officer who had such contrition," Romanucci said. "[Former] Officer Mills, without knowing it, just talked about why we're here, and that's for accountability."

The prosecution told ABC News earlier this month that they will not have any statements until after the trial. The defense attorneys did not immediately respond to ABC News' request for comment.

“The first time I watched the video with my attorney, I couldn’t hold it anymore,” Mills said on Thursday when the prosecution asked him why he pleaded guilty, according to WATN. “I want to make it right.”

Mills agreed with Martin Zummach, Smith's attorney, during cross-examination on Thursday when he asked if the handcuffs, which were secured to one of Nichols' wrists at one point during the encounter, could be considered a deadly weapon and could lead to deadly force being authorized by police, according to WATN. The ex-officer also consented that “necessary force” can be very ugly and violent.

Defense attorneys asked Mills on Wednesday about the use of his baton on Nichols, which Mills said on Tuesday he used to hit Nichols three times the night of their encounter, according to WATN.

Mills claimed that he didn't use the baton to hit Nichols in the head, but admitted that he used it improperly since it's only meant to be used in self-defense, according to WATN. He said it was the first time he ever used his baton or used excessive force on a suspect.

Mills noted that the use of his baton was not because verbal commands weren't working on Nichols when asked by the defense, according to WATN.

Mills disagreed with Bean's attorney when he asked Mills if he was the only one who could intervene to stop the beating, since Mills didn't have his hands on Nichols that night, according to WATN. The ex-officer claimed that the other officers could have moved Nichols away from the strikes and punches while they held his hands.

Mills admitted to the defense that the reason he changed his statement about what happened that night was because he took a plea deal from prosecutors, according to WATN. He said he lied in earlier statements.

Mills told prosecutors that when he told Lt. Dewayne Smith, his former supervisor, that the arrest was done “by the book,” he only said that to hide what really happened, according to WATN. The ex-officer claimed that there was a mutual understanding that their off-camera conversations would go unreported.

“I needed this job for my wife and kids,” Mills said when the prosecution asked why he was not initially truthful about the encounter. “This job has good insurance. I have children with special needs. I needed this job for my family. I let them down."

Mills was asked about response to resistance forms from the incident, stating they weren’t accurate and that Nichols, “was not aggressive at all,” according to WATN.

Mills said that Haley asked him if Mills' body camera captured him during the encounter with Nichols.

“I hope I’m not on there," Mills said Haley told him.

Body-camera footage shows that Nichols fled after police pulled him over on Jan. 7, 2023, for allegedly driving recklessly, then shocked him with a Taser and pepper-sprayed him.

Officers allegedly then beat Nichols minutes later after tracking him down. After the police encounter, Nichols was transferred to the hospital in critical condition.

“I was going along, either way, [with] the cover-up,” Mills said. “Hoping for the best that Mr. Nichols would survive and this whole thing would blow over.”

Nichols, 29, died in the hospital on Jan. 10, 2023. Footage shows the officers walking around, talking to each other as Nichols was injured and sitting on the ground.

Memphis Police Chief Cerelyn Davis said she has been unable to substantiate that Nichols was driving recklessly. The incident triggered protests and calls for police reform.

After the police encounter, Nichols was transferred to the hospital in critical condition. The medical examiner's official autopsy report for Nichols showed he "died of brain injuries from blunt force trauma," the district attorney's office told Nichols' family in May 2023.

The five former officers charged in this case were all members of the Memphis Police Department SCORPION unit -- a crime suppression unit that was disbanded after Nichols' death. All of the officers were fired for violating MPD policies.

“As an officer, I respond to scenes where the victim looks like Mr. Nichols [did after he was beaten]," Mills said. "This was the first time I was a part of it.”

Mills' cross-examination ended Thursday, according to WATN.

ABC News' Deena Zaru and Sabina Ghebremedhin contributed to this report.

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