An 18-year veteran of the US Department of the Interior has resigned in protest from the sprawling federal agency, denouncing “a deeply troubling assault on the rule of the law” that took place at the department under Donald Trump.

John Murdock, an attorney and self-described conservative Christian, began working for the agency’s legal office in 2002. In his resignation letter, first sent to his supervisor earlier this year and obtained exclusively by the Guardian and Public Domain, Murdock cites “glaring legal flaws” he witnessed within the agency during the course of the Trump administration, as well as concerns over offshore oil and gas drilling, the aggressive push to expand fossil fuels and the flouting of environmental regulation.

“We are headed in the wrong direction,” wrote Murdock, who officially stepped down on 30 September.

Murdock’s resignation and public comments come amid an exodus of longtime government workers and scientists within federal agencies, including at the interior department, which has lost thousands of employees ever since Elon Musk’s so-called “department of government efficiency” (Doge) began its controversial efforts to slash government employment last year.