We recommend this article from The Marshall Project: When Warriors Put On The Badge.
The Project investigated whether veterans who became police officers were quicker to resort to force than non-veteran officers. A conclusive answer is impossible given a lack of proper records regarding police violence, but considerable evidence suggests that veteran officers are more likely to get physical in policing situations. The investigation also determined that generally, police departments provide little to no mental health screening or treatment to veteran officers.
The investigation included an analysis of the Boston Police Department. From 2010 to 2015, Boston police officers with military service were more likely than non-veteran officers to receive complaints of excessive force. The Boston Police Department also struggles to recruit officers that reflect the diversity of the city because of Massachusetts’s preference for hiring veterans, who are predominantly white men.