SAN JOSE — A corruption investigation targeting the Santa Clara County Sheriff’s Office over a possible pay-to-play racket for concealed-handgun privileges now has reached the top tier of Sheriff Laurie Smith’s administration, with sources saying her second-in-command — Undersheriff Rick Sung — now is a subject of the wide-ranging probe into whether Smith rewarded political donors with the coveted permits.

Multiple sources confirmed that a search warrant was served Thursday morning at Sung’s office in the Sheriff’s Office headquarters on Younger Avenue in North San Jose. Computer equipment was seized by investigators with the District Attorney’s Office at the direction of its Public Integrity Unit, sources said.

As the investigation intensifies, tension has been building inside the Sheriff’s Office. To date, at least four sheriff’s supervisors — including at least one other high-ranking commander — have been the subject of search warrants in connection with suspected “quid pro quo” handling of the permits, according to sources familiar with the case. The DA’s office previously served a warrant at Sheriff’s Office headquarters in early August.

Sung, who quickly rose to the No. 2 position in the Sheriff’s office in about 16 years, did not immediately respond to calls and messages left for him Friday afternoon. The Sheriff’s Office did not respond to a request for comment in time for the print edition of this story.

Sources also say that multiple concealed-weapon applicants have been interviewed in the case as the DA’s office looks to establish common threads between those who did and didn’t get the permits.

Deputy District Attorney John Chase, who heads the public integrity unit, declined to comment on the search warrant served Thursday but acknowledged the contributions of witnesses to the case.

“We are not going to comment on specifics of our investigation except to thank the many witnesses who have been willing to talk to us and provide evidence voluntarily,” Chase wrote in a statement to this news organization.

A focal point of the DA investigation continues to be a single $45,000 donation by Martin Nielsen, executive protection operations and executive projects manager for Seattle-based AS Solution. Records show Nielsen made the donation in October 2018 to the Santa Clara County Public Safety Alliance, an independent-expenditure committee that backed Smith’s bid for a sixth term, and he and multiple colleagues in the firm received concealed-carry weapon permits this past March.

AS Solution, which specializes in executive security, has said in previous statements that the firm is cooperating with the DA investigation and has launched an internal probe into the matter.

One of the firm’s employees granted a permit along with Nielsen recently took a job with Facebook, currently one of AS Solution’s most prominent clients. Facebook spokesperson Anthony Harrison confirmed that AS Solution “is one of at least a dozen security providers we use.”

When asked whether Facebook founder Mark Zuckerberg and Sheryl Sandberg were among those protected by AS Solution, which first was reported by San Jose Inside, Harrison gave a more general answer.

“Our security partners provide protection services for several key executives, including Mark and Sheryl,” Harrison wrote in an email.

While a firm could more easily obtain what are known as “guard cards” and accompanying firearm permits from the state Bureau of Security and Investigative Services, those require firearms to be exposed — as in a visible holster — and the guard be in uniform.

A CCW permit, however, allows a security provider to be more discreet, which high-profile clients prefer. Harrison said Facebook did not play a role in securing permits for Nielsen and his colleagues.

The county has been long criticized for its lack of public transparency on how many applications are received and rejected and is the target of at least one active civil lawsuit over how the privilege is granted. CCW permits in California are issued at the sole discretion of the state’s sheriffs and police chiefs, and their sensibilities range widely. Santa Clara County tends to issue fewer permits than most of the state’s 58 counties, particularly those outside of the Bay Area.

Currently, only about 150 such permits have been issued or renewed in Santa Clara County since 2014. San Bernardino County, which has a similar population albeit stretched over a far larger geographical area, has over 3,000 active permits. And Sacramento County, which has 20 percent fewer people than Santa Clara County but is similar in its urban and suburban mix, has over 5,000 such permits issued to residents.