Brian Trainor, the No. 2 official in the St. Tammany Parish Sheriff’s Office, announced Monday that he’s running for district attorney of the 22nd Judicial District, which covers St. Tammany and Washington parishes.

He becomes the first candidate in the race who has worked under the current DA, Walter Reed, who has held the job for nearly 30 years.

Trainor, the chief deputy in Sheriff Jack Strain’s office, went to work there in 2010. Before that, he spent eight years in Reed’s office, where he prosecuted thousands of cases, according to a news release announcing his candidacy.

Trainor, a Republican, touts his law enforcement experience both as a prosecutor and with the Sheriff’s Office.

“My promise to the public is that I will be at work and accessible to the public every day of the week with the goal of ensuring fairness and justice for all,’’ Trainor said in an apparent slap at Reed, who has been criticized for inaccessibility and allegedly frequent absences from the office.

Reed, who filed a campaign finance report in May, has yet to say whether he plans to seek a sixth term. Qualifying begins Aug. 20 for the Nov. 4 primary.

If he does run, he’ll face opposition for the first time since 1996 — in fact, not just one challenger but at least three. Covington lawyer http://www.theneworleansadvocate.com/home/9443584-172/hopefuls-starting-to-line-up">Roy Burns, who served as an assistant district attorney under Reed’s predecessor, Marion Farmer, and Slidell attorney http://theadvocate.com/news/neworleans/neworleansnews/9700101-123/gusman-airbrushes-out-the-blemishes://">Alan Black both have announced they are running.

The expanding field follows weeks of negative news for the incumbent, who is under investigation by a federal grand jury. Last week, he hired public relations consultant http://www.theneworleansadvocate.com/news/9681228-171/tammany-da-walter-reed-lashes">Morgan Stewart to handle questions concerning his outside business interests, campaign finance matters and his family — all issues that have been the subject of recent news coverage.

FBI agents visited Reed’s office last month, and in May, a federal grand jury http://theadvocate.com/news/9365786-123/subpoena-shows-feds-are-scrutinizing">subpoenaed documents from the Castine Center in Mandeville related to a campaign fundraiser that Reed held there. His son, Steven Reed, was paid with campaign funds for services for that event that remain unclear.

http://theadvocate.com/news/neworleans/9505892-148/another-subpoena-issued-surrounding-tammany">Leo Hemelt, an assistant district attorney who notified his superiors that he intends to retire Aug. 1, also has been subpoenaed, according to sources. Hemelt filled in for Reed at meetings of the board of St. Tammany Parish Hospital, which paid Reed $30,000 a year for providing legal advice.

Reed, who resigned from the hospital job in May, has said that his work for the hospital was as a private lawyer, but hospital officials characterized the arrangement as being with the District Attorney’s Office. It’s unclear how Hemelt was paid for his services.

Follow Sara Pagones on Twitter, @spagonesadvocat.