Washington — Homeland Security Secretary Alejandro Mayorkas has launched an internal investigation to address the threat of domestic violent extremism within the department, according to a memo to employees obtained by CBS News. In the message to Department of Homeland Security (DHS) employees on Monday, the secretary wrote that “recent events, including the January 6th attacks on the U.S. Capitol, have highlighted that domestic violent extremism poses the most lethal and persistent terrorism-related threat to our country today.” Mayorkas called rooting out domestic violent extremism an “urgent priority of the Biden-Harris Administration and of this Department.” The secretary has instructed a cross-agency, internal working group to complete a “comprehensive review of how to best prevent, detect, and respond to threats related to domestic violent extremism within DHS,” led by chief security officer Richard McComb, according to DHS. “Violent extremism has no place at DHS and we will work with urgency and focus to address it,” Mayorkas wrote in his message to employees. “Just announcing it sends a very important signal, not only to the DHS workforce, but to the broader community that DHS does not just have a mission to domestic extremism outwardly,” retired U.S. Marine colonel Dave Lapan, who served as DHS press secretary during the Trump administration, told CBS News. “It’s also making sure that it’s own house is in order.” Lapan compared the internal review to the service-wide, 60-day “stand down” within the U.S. military, ordered in February by Defense Secretary Lloyd Austin. “It is similar to the DOD,” Lapan said. “A significant portion of DHS is law enforcement agencies and we know that extremists groups try to recruit from both law enforcement and the military. It makes sense that DHS would also take that internal look.” Earlier this month, Austin also established a working group centered on extremism in the ranks. CBS News has reported at least 42 current or former military members have been arrested in relation to the attack on the Capitol on January 6. Elizabeth Neumann, the former assistant secretary of counterterrorism and threat prevention for DHS, told CBS News that as the third-largest government agency, DHS is “statistically” at risk of harboring individuals with extremist viewpoints. “It’s a 240,000 person organization,” Neumann said of DHS. “Statistically speaking, there are going to be people that hold viewpoints that might be extremist and might also make them vulnerable to being recruited by extremists. Of course, holding these viewpoints is not illegal,” she added. “But you give up certain rights when you swear an oath and become a government employee.” Thomas Warrick, former DHS deputy assistant secretary for counterterrorism policy, said the department possesses “special challenges” addressing white supremacism. “Unlike the Department of Defense, where the culture is built around the chain of command, DHS is largely federated, with components that historically have a great deal of day-to-day autonomy.” The former DHS senior official said that even a small number of “problematic officers” can be “corrosive” to the institution at large. The internal probe follows the arrest of a former Coast Guard lieutenant, Christopher Hasson, who in February 2019 was accused of compiling a hit list of Democratic politicians and media personalities. Hasson, who described himself as a “long time White Nationalist” in emails obtained by prosecutors was later sentenced to more than 13 years in prison after agents found seven rifles, two shotguns, four pistols, two revolvers, an assembled firearm silencer, a disassembled firearm silencer, magazines, and hundreds of rounds of ammunition at his home. The revelation of such profound extremism inside the U.S. Coast Guard, which sits under the purview of DHS, helped spur a September 2019 strategy bulletin issued by then-acting DHS Secretary Kevin McAleenan. The department called for the prevention of insider threats as a “priority action,” in its report, noting, “criminal and terrorist networks recruit and coerce corrupt or vulnerable personnel employed by government and transportation stakeholders.” The report continued, “These individuals possess insider privileges and knowledge that can facilitate, on behalf of the hostile organization, intelligence-gathering and counter-surveillance activities; theft; smuggling; tampering with or sabotaging security systems and devices; and, in some cases, terrorist attacks.” But earlier in April 2019, DHS acknowledged key changes in its intelligence gathering, admitting that it “restructured” the team that once fed information about domestic terrorism and white supremacist groups to local police departments. Former DHS officials told CBS News at the time that the unit responsible for tracking homegrown terrorism was “gutted” at the worst possible moment – just as domestic threats and white supremacist groups had begun to spike. “This is not brand new,” said Neumann, who served at the Department of Homeland Security from 2017 to April 2020, on Monday. “For two years, we’d had conversations in the department about how to do this better.” But the former DHS official commended Secretary Mayorkas for clearly communicating the investigation into domestic violent extremism as a “priority” within a behemoth of an agency also responsible for tackling issues of immigration, cybersecurity and disaster response. McComb will work in close coordination with Homeland Security’s Privacy Office and Office for Civil Rights and Civil Liberties, among others, according to a DHS official. The panel of senior DHS personnel is expected to submit a report with recommendations to the Secretary, though the timeline remains unclear. Notably absent from the review is the Department of Homeland Security’s Office of the Inspector General. A recent preliminary review by the Government Accountability Office found DHS’ top watchdog plagued by chronic professional misconduct and longstanding dysfunction within its ranks. The announcement comes just before President Biden’s Wednesday address to a joint session of Congress, which is deemed a National Special Security Event (NSSE) by U.S. Secret Service. DHS’ assistant Secretary for Counterterrorism and Threat Prevention John Cohen is also slated to testify on Capitol Hill, on Thursday on racially and ethnically motivated violent extremism. Over the weekend, the Department of Homeland Security quietly extended its National Terrorism Advisory System (NTAS) bulletin warning the public of a “heightened threat environment” across the United States. The first wholly domestic terrorism bulletin issued following the presidential inauguration and violent assault on the U.S. Capitol was set to expire at the end of April, but was pushed back by the secretary to May 15, 2021, granting officials two extra weeks to reassess the current threat environment. Jeff Pegues and Eleanor Watson contributed to this report.