The cloud that began forming two weeks ago over Honolulu’s Department of the Prosecuting Attorney is getting darker as its elected chief remains tight-lipped on a matter of legitimate public interest.

In the aftermath of reports that he received a letter warning that he’s a target of a federal probe, city Prosecuting Attorney Keith Kaneshiro has failed to offer a much-needed, no-nonsense explanation as to what’s going on and what’s in the works, if anything, to shield the office from the investigation’s taint.

The silence lingered this week, as a Honolulu businessman filed an impeachment petition — with 861 signatures — against Kaneshiro in state Circuit Court. Certification of 500 registered voters is needed to proceed with impeachment on grounds of malfeasance (wrongdoing), misfeasance (a transgression) or nonfeasance (failure to perform an act required by law).

Among the petition’s most compelling arguments: Failure to take reasonable or necessary administrative action against Kaneshiro’s former deputy, Katherine Kealoha, to protect the integrity of any prosecution she was involved in after it became known the FBI was investigating her for potential criminal wrongdoing.

Two of Kaneshiro’s top deputies, Chasid Sapolu and Janice Futa, reportedly received subject letters — noteworthy, but less serious than Kaneshiro’s target letter. Sapolu confirmed his letter last week, and did the right thing by placing himself on leave. Futa has remained mum.

So has Kaneshiro — who should step up by stepping away from the office while the probe runs its course.