Fact

To this day there is very little information on that kid.

The original poster makes a valid point; black areas are associated with high gun crime rates. Despite accounting for only 14% of the U.S. population, Black people account for 60% of those killed by firearm homicide each year. On average, Black people are over 11.5 times more likely to be victims of firearm homicide than their non-Hispanic white peers. https://www.bradyunited.org/resources/research/disproportionate-impact-gun-violence-black-americans

Trickly down is what the non-thinking left wing calls it.

Do you mean supply-side economics? Supply-side economics is a macroeconomic theory postulating that economic growth can be most effectively fostered by lowering taxes, decreasing regulation, and allowing free trade.[1][2] According to supply-side economics theory, consumers will benefit from greater supply of goods and services at lower prices, and employment will increase.[3] Supply-side fiscal policies are designed to increase aggregate supply, as opposed to aggregate demand, thereby expanding output and employment while lowering prices. Such policies are of several general varieties: Investments in human capital, such as education, healthcare, and encouraging the transfer of technologies and business processes, to improve productivity (output per worker). Encouraging globalized free trade via containerization is a major recent example. Tax reduction, to provide incentives to work, invest and take risks. Lowering income tax rates and eliminating or lowering tariffs are examples of such policies. Investments in new capital equipment and research and development (R&D), to further improve productivity. Allowing businesses to depreciate capital equipment more rapidly (e.g., over one year as opposed to 10) gives them an immediate financial incentive to invest in such equipment. Reduction in government regulations, to encourage business formation and expansion.[4]

Can they replicate the propagation conditions?

What is ‘Trickle Down’?