Neither of those sources prove that BLM is only about white on black murder. Check out this source if you are interested in learning about the goals of BLM https://blacklivesmatter.com/about/
But it's nuanced and more than can be defined on a page with vast sub cultures and groups all lobbying for power.
As is any social movement, I think there are some problems inherent with it, like the inability to criticize aspects of the movement without being considered a racist.