This doesn't seem to be true. According to Wikipedia, there were 2340 domestic homicides in 2007.[1] There were 18,361 homicides that year.[2] So <13% of homicides were domestic. You may have read a statistic that most women killed in homicides are killed by romantic partners - but this is not true of men, who are the overwhelming majority of homicide victims.
Even if the rate of domestic homicides doubled it would mean only a 13% increase in the overall homicide rate, far less than what we've actually observed.
> people were home more and under a lot of stress.
This explanation does not seem to fit with the social mobility data presented. The pandemic struck in March, people were staying home far more in March/April/May than in June - but homicides did not rise until June. Why?
> An increase in murder can just mean the same number of people shooting each other as normal, but more of them died.
It could mean that. But no: shootings and shooting victims increased dramatically right along with murders:
- in Chicago: https://abc7chicago.com/chicago-shootings-2020-shooting-crim...
- in NYC: https://www.wsj.com/articles/new-york-city-homicides-and-sho...
- in Portland: https://www.koin.com/news/crime/shootings-in-portland-more-t...
[1] https://en.wikipedia.org/wiki/Domestic_violence_in_the_Unite...
[2] https://www.cdc.gov/mmwr/preview/mmwrhtml/su6203a28.htm?s_ci...
In places like Toronto and London homicides decreased in 2020 while they increased in major US cities.
This isn't necessarily the actual explanation, but you can't decide between this and competing hypotheses without analyzing the nature of the homicides that happened. Were the increases mostly due to gangs and ruffians shooting each other on the street? Or were they mostly due to people at home shooting their spouses and kids?
Don't forget the huge jump in unemployment as well. Unemployed people tend to commit more crimes. So why not burglary? Well again, if people are home, it's a lot harder to burglarize them. Why not drug crime? A whole lot of drug use was legalized in the past year, so you don't want to look at drug crime, you want to look at drug usage.
There's also hospital overcrowding. An increase in murder can just mean the same number of people shooting each other as normal, but more of them died. Did attempted murder also increase? I don't even see that question asked.
I obviously don't have any answers because I haven't done the analysis either, and I'm not going to because I'm not a journalist or analyst and already have a job, but the people whose job is to do this kind of analysis should at least do it correctly.