I think there’s clear evidence that the current murder spike was caused primarily by the 2020 BLM protests. The timing matches the protests well, and the pandemic poorly. The spike is concentrated in black communities and not in any of the other communities affected by the pandemic. It matches homicide spikes corresponding to other anti-police protests, most notably in the cities where those protests happened but to a lesser degree around the country. And the spike seems limited to the US, while other countries had basically stable murder rates over the same period.
I agree with Scott Alexander, although I would emphasize a little more the mediating factor of the police pullback.
I would also add that each step in the mechanism–protests lead to police pullback which leads to an increase in murders–is well supported on its own in the academic literature. Step one, for example, is that protests lead to police pullback. In The effect of highly publicized police killings on policing: Evidence from large U.S. cities Cheng and Long document exactly this:
Our regression discontinuity and difference-in-differences estimates provide consistent and strong evidence that those high-profile killings reduced policing activities, including police self-initiated activities and arrests.
That’s step one. Step two is that police on the street reduce crime which you can find from my research using the terror alert level as well as that of many others. Step one plus step two leads to a spike in murders following the 2020 BLM protests.
As Alexander noted, we also have plenty of evidence on a micro level. For example, I showed clear evidence of police pullback–a “blue strike”–and consequent increase in crime in Baltimore after the Freddie Gray protests. Put it all together along with the timing and other evidence and the case is strong that the 2020 BLM protests led to police pullback which led to a spike in murders, especially in black communities.