Retired Police Officer Sentenced to 60 Months in Federal Prison for Obstructing Justice

News Release from U.S. Attorney's Office, Districts of Guam & the Northern Mariana Islands, Thursday, April 24, 2025

Hagåtña, Guam – SHAWN N. ANDERSON, United States Attorney for the Districts of Guam and the Northern Mariana Islands, announced that defendant, John T. Mantanona, age 67, was sentenced by designated Senior District Judge John C. Coughenour in the District Court of Guam to 60 months imprisonment for Obstructing Justice by Endeavoring to Influence a Juror, in violation of 18 U.S.C. § 1503.  The Court also ordered two years of supervised release, a $30,000 fine, and a mandatory $100 special assessment fee.

From October 12, 2018, through November 13, 2018, Chief Judge Frances Tydingco-Gatewood conducted a federal jury trial in the criminal case of United States v. Raymond Martinez and Juanita Moser, 15-CR-00031.  Mantanona was retired from the Guam Police Department, including work as an FBI task force officer.  Martinez and Moser hired him as an investigator during the trial.  Mantanona tried to influence Gregorio Tyquiengco while Tyquiengco served as a juror in the case.  During the trial, and prior to jury deliberations, Mantanona contacted Tyquiengco to discuss what verdict Tyquiengco would render and to influence him to vote “NG” (not guilty) despite the evidence against Martinez and Moser.  Mantanona also wanted Tyquiengco to persuade other jurors to do the same, with the intent to cause a hung jury and mistrial.  A mistrial was declared on November 13, 2018.  Mantanona met with Tyquiengco and gave him $1,000, in addition to $100 afterward.

Tyquiengco pled guilty to Contempt of Court, in violation of 18 U.S.C. § 401(3).  He was sentenced to 30 days imprisonment and one year of supervised release. Tyquiengco was also ordered to reimburse the district court for any money he received for serving as a federal juror.

William Topasna Mantanona pled guilty to False Statement to Government Agent, in violation of 18 U.S.C. § 1001(a)(2). During a wiretapped telephone conversation, he communicated with his brother, John T. Mantanona, to facilitate the above-described scheme.  He later falsely denied this conduct during an investigative interview with a special agent from Homeland Security Investigations.  On August 26, 2021, the district court sentenced William Topasna Mantanona to six months imprisonment, two years of supervised release, and a mandatory $5,000 fine.

“The public should have faith in our justice system, which includes fair and impartial court proceedings.  Mantanona violated this fundamental concept of trial by jury.  The Department of Justice will hold accountable those who obstruct justice," stated United States Attorney Anderson.   "I applaud our law enforcement partners for pursuing an investigation beyond the initial crimes by Martinez and Moser.”

"Great trust is placed in those who call law enforcement their mission," said Homeland Security Investigations Hawaii Special Agent in Charge Lucy Cabral-DeArmas. "Violating that trust by working to dilute the integrity of our judicial process is a complete betrayal of that mission and brings down every person who seeks to serve the public.  This sentence sends a clear message to those currently in or retired from law enforcement that if you break that trust, there will be consequences."

“The FBI’s anti-corruption work remains one of our highest priorities. Those who criminally influence jurors and their deliberations through bribery strike at the very foundation of our criminal justice system,” said FBI Honolulu Special Agent in Charge David Porter. “Mr. Mantanona tampered with the integrity of our legal process, and in so doing, attempted to deny our community the justice it deserves. As reflected by this investigation, the FBI is committed to protecting our legal system and will bring to justice those who act to corrupt it.”

“While this conviction is for obstructing justice, this is a direct result of a firearms trafficking case from a number of years ago in which we seized more than $1.2 million in cash, $2 million more in additional seizures, and 67 firearms,” said ATF Seattle Special Agent in Charge Jonathan Blais.  “It’s discouraging to see that a retired law enforcement officer was involved in these illegal actions, but we are glad to see the passing of this sentence.”

This case was investigated by the Federal Bureau of Investigation, Homeland Security Investigations, and the Bureau of Alcohol, Tobacco, Firearms & Explosives.

Assistant United States Attorney Rosetta L. San Nicolas prosecuted the case in the District of Guam.

The case was investigated under the Organized Crime Drug Enforcement Task Forces (OCDETF). OCDETF identifies, disrupts, and dismantles the highest-level criminal organizations that threaten the United States using a prosecutor-led, intelligence-driven, multi-agency approach. For more information about Organized Crime Drug Enforcement Task Forces, please visit Justice.gov/OCDETF.