A special prosecutor appointed from the U.S. Attorney’s Office in San Diego has launched a criminal probe into Honolulu Police Chief Louis Kealoha and his wife, Katherine, a high-ranking city prosecutor.

Assistant U.S. Attorney Michael Wheat is directing the federal investigation, and working with the FBI. He declined to comment on the case.

The investigation, which will include subpoenas and secret grand jury proceedings, revolves around a mailbox that was stolen from the Kealohas’ house in 2013, and allegations that the chief and his wife tried to frame her estranged uncle for the crime.

Wheat is based at the U.S. Attorney’s Office in San Diego. He has worked as a prosecutor for the U.S. Department of Justice for 30 years, and has handled a variety of criminal prosecutions, including cases of alleged prison rape, drug smuggling and human trafficking.

In 2005, Wheat was a lead prosecutor in a public corruption case involving the acting mayor of San Diego and a city councilman who were convicted of performing political favors  for a local strip-club owner who was donating to their campaigns.

Few details have emerged about the scope of the federal investigation into the Kealohas. What’s known is that it all started with a missing mailbox.

Katherine Kealoha accused her uncle, Gerard Puana, of stealing her mailbox in 2013, telling authorities that she saw him on surveillance video throwing it into a car. A special unit of Honolulu police officers investigated the case and arrested Puana. He was eventually charged with a federal crime.

But during Puana’s trial, his federal public defender, Alexander Silvert, said the man Katherine Kealoha identified in the video was not his client. Silvert said he planned to lay out a conspiracy theory during the trial that showed the investigation was a set-up.

The trial ended, however, when the chief took the stand and testified about Puana’s criminal past, in violation of court rules. A mistrial was declared and Silvert met with federal prosecutors to share his evidence of a possible frame job.

The U.S. Attorney’s Office permanently dismissed the case against Puana and forwarded the matter to the FBI for further investigation.

Silvert told Civil Beat this week that he can’t comment on the specifics of the case, but said that he’s pleased with the direction it’s heading. He also said he believes the investigation will go beyond the mailbox theft, although he refused to explain why, other than saying he had turned up other “improprieties” during his pre-trial research.

“If I did not think that the investigation was going to be taken seriously I would have come forward a long time ago to discuss the evidence I had,” Silvert said. “But because I do believe it is being taken seriously and I believe that something will come out of this, I’m willing to remain quiet for the time being to let the process work.”

State Sen. Will Espero has been pushing his colleagues to implement sweeping police reforms in the face of well-documented cases of corruption and misconduct at HPD.

Espero’s proposals haven’t gained much traction in the Legislature. But he hasn’t shied away from criticizing the Honolulu Police Commission or other top city officials for not doing anything, including Mayor Kirk Caldwell, who declared the issue “a private matter.”

The senator has called on the commission to place the police chief on leave, which is typically what happens when officers are under investigation for misconduct. The commission is scheduled to meet next week to discuss the issue behind closed doors.

“The trust and confidence that residents have in the department and the leadership has been strained,” Espero said. “It’s sad that we’re in this dilemma today, and I know that people in the department, their morale is down. They aren’t happy.”

The Kealohas are also under a city ethics probe for their involvement in the mailbox case. The couple has sued the Honolulu Ethics Commission in an attempt to stop the investigation.

Both Louis and Katherine Kealoha declined to comment.