SDG #16 is to “Promote peaceful and inclusive societies for sustainable development, provide access to justice for all and build effective, accountable and inclusive institutions at all levels”
Within SDG #16 are 12 targets, of which we here focus on Target 16.4:
By 2030, significantly reduce illicit financial and arms flows, strengthen the recovery and return of stolen assets and combat all forms of organized crime
Target 16.4 has two indicators:
Indicator 16.4.1: Total value of inward and outward illicit financial flows (in current United States dollars)
Indicator 16.4.2: Proportion of seized, found or surrendered arms whose illicit origin or context has been traced or established by a competent authority in line with international instruments
Illicit financial flows are money movements which fit into a variety of categories of criminality. This may be due to where the money's originated, whether it's avoiding taxation, or what its financing.
Of relevance to the first indicator is the UN Convention Against Corruption. All member states of the UN are party to this treaty except Eritrea and North Korea, and Syria has signed but not ratified.
For the second indicator, one of the relevant UN bodies is the UN Office for Disarmament Affairs. Also of relevance is the work of Interpol (International Criminal Police Organization), which isn’t part of the UN System.
There’s an unfortunate great dearth of data for both indicators of this target.