Los Angeles County Sheriff Jim McDonnell has launched a comprehensive inquiry into secret deputy cliques and is looking into whether gangs that condone illicit behavior are operating within his ranks, he said Thursday.

McDonnell’s announcement at a meeting of the Sheriff Civilian Oversight Commission comes two weeks after allegations surfaced that as many as 20 deputies at the Compton Station have matching tattoos featuring a skeleton holding a rifle, reports the Los Angeles Times.

A Compton deputy recently admitted under oath that he was inked with the skull logo in June 2016, about two months before he was involved in a fatal shooting, the Times reported.

McDonnell, who was elected in 2014 on a promise to reform a corrupt agency, said he is partnering with the Sheriff’s Inspector General and county counsel to study why the groups form, whether they are exclusive, if members are required to act a certain way, and if they endorse bad behavior.