The most significant point of reform was in 2001, with the complete replacement of the RUC, but change began much earlier. A key factor of police brutality in the years before and during the Troubles was the existence of B-Specials, a police reserve known for its viciousness and lack of training; these were often seen as thugs for hire, people that weren’t interested in being professional law enforcement officers and signed up simply to beat up Catholics and earn a bit of cash as an added bonus. Notably, they were largely recruited from existing loyalist paramilitaries and had even less Catholic representation than the police regulars. This force was abolished in 1970 upon the recommendation of the Hunt Report, which also recommended increased recruitment of Catholics, though this was mostly unsuccessful, at least in part due to a lack of support from political nationalists and death threats from the (Provisional) IRA towards Catholics who joined; although things have improved since the abolition of the RUC, the force continues to struggle to recruit Catholics at desired levels. For an idea of numbers, the force was 92% Protestant in 2001, compared to about 70% Protestant in 2011 (despite being only 48% of the population in the 2011 Census), after years of attempted 50/50 recruitment quotas. In referring to Troubles-era efforts, it is worth remembering that the deployment of the British Army to Northern Ireland was at least partly an attempt to reign in police brutality. For the policies which influenced the creation of the RUC, the key document is the Patten Report. I’ll list some of the key changes:

1. The name: many Catholics are alienated by royal symbolism, as shown by the refusal of many Catholic politicians to swear oaths to the Queen. Furthermore, the use of “Ulster” as an alternative term for Northern Ireland is inflammatory to many Catholics, particularly as it’s viewed as inaccurate: the traditional province of Ulster comprises 9 counties, not the 6 of Northern Ireland. These changes were part of a broader removal of loyalist, British symbolism

2. Accountability: the creation of an Ombudsman and Complaints Tribunal, to ensure that police wouldn’t be above the law or protected by the blue code

3. A new pledge, with a greater focus on human rights

4. Emphasis on community policing: this one is tricky to explain. Essentially many areas of Northern Ireland, particularly in areas like North Belfast, are not necessarily accessible places for police to operate. Police therefore rely heavily on collaboration with community organisers, often nationalist politicians with paramilitary connections and thus clout in their local neighbourhoods. When the police try to interfere in these areas without the support of these community leaders, is is normal for police to be met with intense resistance, including rioting, destruction of evidence, silence, and brick and petrol bomb attacks.

The support of other organisations also played a role in the effectiveness of the transition: Sinn Fein eventually endorsed the new police force, which was a significant step in changing the attitudes of many Catholics, as was the GAA’s repeal of Rule 21, which banned any member of British police or military from being a GAA member (the Gaelic Athletic Association, if you aren’t familiar with it, is a sports governing body that plays a large role in Irish Catholic culture). Equally vital were stronger links with the Southern Irish police force, which allowed for cross-border operations, with a high-profile case being that of the raid on the farm of Thomas “Slab” Murphy (a senior Republican), which straddled south Armagh and Louth, counties either side of the border. Before that, it had been relatively easy to stockpile weapons and simply shift them to the other side of the border if you were tipped off about an impending raid; only closer collaboration between jurisdictions closed this loophole.

It would be dangerous to draw overly close parallels with the situation in Northern Ireland and that in Minneapolis (internment, for example, was a huge complicating factor in that police had an enormous range of legal powers that the Minneapolis Police Department couldn’t dream of having, and judicial rights in general were limited for Catholics - an example being Diplock courts, only abolished in 2007, in which Republicans accused of violence weren’t entitled to a trial by jury), and actually much of my answer breaks this subreddit’s 20-year rule, though I doubt it would be possible to even attempt an earnest answer to this question while observing that rule, so it might be worth posting this question in a different subreddit; many Northern Irish people will have far more in-depth knowledge of this than me (much of what I’ve written is taught at age 15-16 in Northern Irish schools), and another subreddit might provide more room for personal stories and anecdotes which help illuminate the realities of policing in Northern Ireland during the Troubles.