More than a year ago, four Houston Police Department officers were relieved of duty as part of an investigation for potentially falsifying citations, allegations that accused them of listing themselves as witnesses on incidents they did not see or that did not occur. That same day, one of the officers was found dead in an HPD parking garage from a self-inflicted gunshot wound.

On Thursday, 15 months after an internal affairs investigation led to the administrative action, the last officer to go to trial in the case admitted guilt.

Robert Manzanales, the senior officer with 20 years on the job, pleaded guilty to tampering with an official document and aggravated perjury. He was given deferred adjudication, a form of probation. If he successfully completes three years of probation, he will not have the conviction on his record.

His plea on Thursday mirrored those of his former colleagues Gregory Rosa and John R. Garcia, who also admitted guilt and were given the same terms of punishment. Rosa was also charged with perjury. Garcia was not.

Manzanales, 47, did not comment Thursday after he was sentenced by state District Judge Michael McSpadden during a brief hearing.

His attorney, Scott Siscoe, said the former officer just wanted to put the matter behind him.

The Houston Police Department did not answer questions about the scam but on Thursday released a statement from Chief Charles McClelland saying Manzanales' conduct was thoroughly investigated by the department.

"It is important to remember that one person's actions are not reflective of the vast majority of the men and women of the Houston Police Department that conduct themselves professionally," McClelland said in the statement.

Ray Hunt, president of the Houston Police Officers Union, said the union did not represent any of the officers in the legal proceedings and declined to comment further.

The four officers were involved in a scheme to claim overtime for appearing in court outside of regular work hours, according to a source familiar with the investigation. It was not known how much money was claimed.

Typically, officers can collect overtime in traffic cases when they are subpoenaed to appear in municipal court at a time that is outside of their duty hours. If an officer assigned to an overnight shift wrote a ticket during his work hours, then appeared for a daytime court date, he would be compensated with overtime.

By falsely listing each other as witnesses, they could all claim overtime for coming to court.

After the investigation, city prosecutors dismissed hundreds of traffic tickets written by the four officers, who worked in the traffic enforcement division, saying the allegations and an internal probe made the integrity of the citations questionable.

The four were relieved of duty on Aug. 19, 2014. Later that day, Rudolph Farias III was found dead in a patrol car in a downtown police parking garage. Farias, who had been with the department since 1993, was dressed in uniform.

In January, Rosa and Garcia resigned, and Manzanales retired. The same month, a Harris County grand jury indicted them.

After the indictment, McClelland said an investigation did not show any evidence that a systemic problem exists in the police department.

The ticket rigging case was the second within two years at the department. In 2012, four veteran officers who collected nearly $1 million in overtime pay over several years were suspended for listing one another as witnesses on traffic tickets. Their punishments ranged from 20 to 45 days off without pay.