While I can't speak to the specific offenders in these cases, I can say that statistically murder victims of all races are overwhelmingly killed by members of their own race. So blacks tend to kill blacks, whites tend to kill whites, etc. Of course these are general trends, not hard and fast rules but I see no evidence to suggest that Boston is some sort of outlier.

https://www.reuters.com/article/uk-factcheck-data-racial-murder/fact-check-false-data-on-u-s-racial-murder-rates-idUSKCN24I2A9

From the article:

According to the FBI’s Expanded Homicide data from 2018, the most recent report of this kind Reuters was able to find ( here ), 80.7% of the murders of white people were committed by white offenders (2,677 of a total of 3,315) while 15.5% of the murders of white people were committed by Black offenders (514).

The social media post also alleges white offenders committed 2% of the murders of Black victims. According to the FBI’s data, 8% of the reported murders of Black people were committed by white offenders (234 of a total of 2,925) and 88.9% by Black offenders (2,600).

FBI data from 2017 also follows this trend: 80.2% of white victims were killed by white offenders, 8.9% of Black victims were killed by whites, 88.5% of Black victims were killed by Blacks, and 16.1% of whites were killed by Blacks ( here ).