In stark contrast, all investigations that were preceded by "viral" incidents of deadly force have led to a large and statistically significant increase in homicides and total crime.

 From Policing the Police: The Impact of "Pattern-or-Practice" Investigations on Crime by Tanaya Devi.  From the Abstract:

This paper provides the first empirical examination of the impact of federal and state "Pattern-or-Practice" investigations on crime and policing. For investigations that were not preceded by "viral" incidents of deadly force, investigations, on average, led to a statistically significant reduction in homicides and total crime. In stark contrast, all investigations that were preceded by "viral" incidents of deadly force have led to a large and statistically significant increase in homicides and total crime. We estimate that these investigations caused almost 900 excess homicides and almost 34,000 excess felonies. The leading hypothesis for why these investigations increase homicides and total crime is an abrupt change in the quantity of policing activity. In Chicago, the number of police-civilian interactions decreased by almost 90% in the month after the investigation was announced. In Riverside CA, interactions decreased 54%. In St. Louis, self-initiated police activities declined by 46%. Other theories we test such as changes in community trust or the aggressiveness of consent decrees associated with investigations -- all contradict the data in important ways.

 The almost 900 excess deaths are over the following two years of a viral driven investigation and is only for those particular cities.  There is a lot of important information or analysis not done but the broad issues are apparent in these case studies.

For the five investigations that were sparked by nationally visible incidents of deadly use of force – Baltimore, Chicago, Cincinnati, Ferguson and Riverside– investigations cause statistically significant increases in both homicide and total crime. Contrary to other investigations, investigations during this time lost lives – 179 of them, per investigation, in the 24 months following the start of the investigation. That’s 893 total. Almost 900 individuals whose potential may not have been realized. And, we are still counting. A back-of-the-envelope calculation suggests that these five cities converge to pre-investigation levels 51 months after the investigation and, by that time, almost 1214 excess homicides will have occurred.

These cities are grossly variable in size but, crudely, cities conducting investigations of "viral" incidents  experience nearly an increase of nearly 250 deaths and 9,200 felonies before returning to normal after roughly 50 months.   

In contrast,

For investigations that are sparked by mostly civilian complaints, allegations, lawsuits or media reports of excessive force, investigations caused a statistically significant decline in homicide and total crime rates. These investigations saved lives – 61 per investigation, in the 24 months following investigations.

City leaders have a choice.  Review and reform early in the normal course of incidents or wait to do investigations and reform after a viral event.  The former approach costs money and ruffles feathers but saves 60 or so lives.  The latter approach is tactically easier but costs 250 excess deaths among citizenry and 9,200 felonies.   Much of which fall on marginalized communities.

No matter how sincere the arguments from reformers, if they conduct their reviews after viral events, their actions are costing 250 citizens' live.