If you are interested in mental illness and gang membership, perhaps this BBC report and the related journal article may be of interest:
“Young men in gangs are significantly more likely to suffer from a mental
disorder and need psychiatric help than other young men, says a UK study”.
“Prof. Jeremy Coid, lead study author and director of the forensic psychiatry research unit at Queen Mary, University of London, explained the likely cause:
It is probable that, among gang members, high levels of anxiety disorder and psychosis were explained by post-traumatic stress disorder, the most frequent psychiatric outcome of exposure to violence”.