Alex G. Tse, a longtime federal prosecutor who once worked in the San Francisco City Attorney’s Office, has been named acting U.S. Attorney for the Northern District of California, in the wake of his boss’s resignation.

Tse officially assumed the post Sunday after Brian Stretch, who had been in the job for nearly two years, stepped down last week to join a private firm, according to a news release from the U.S. Attorney’s Office.

Tse had been serving as First Assistant U.S. Attorney — the district’s second-in-command — since 2016, after heading the office’s civil division for about three years. From 1994 to 2006, he worked in the office as a rank-and-file federal prosecutor. Between those periods, he served a six-year stint as a deputy city attorney in San Francisco.

Stretch, whose resignation was announced Thursday, will join Sidley Austin LLP in its San Francisco office as a partner in its white collar, government litigation, and investigations practice.

U.S. Attorneys, who are appointed by the president and confirmed by the Senate, can be known to step down upon the election of a president different from the one who selected them. Whether Tse ends up with the permanent position is unclear; the Justice Department has a process that it will undergo in order to determine his replacement, U.S. Attorney’s Office spokesman Abraham Simmons said.

The change-up occurred as U.S. Attorney General Jeff Sessions rescinded the Cole Memo, an Obama-era rule that essentially discouraged federal prosecution of marijuana laws, and would encourage U.S. Attorneys to exercise their own discretion in prosecuting cannabis cases.

Tse earned a bachelor’s degree from UC Berkeley in 1987 and received his law degree from UC Hastings College of Law in San Francisco in 1990.