Engels was accusing the capitalist or bourgeois class of committing social murder. It's important to be clear that when he says bourgeois, he is not talking about middle-class people. He means the people who are not aristocrats, but who are at the very top of industry: what we might call the one percent or one-tenth of the one percent.
His point in this book is to expose the hidden lives of the working class. He notes that much poverty and misery is hidden behind house fronts that don't look so bad. First, the rich in England in that time lived in beautiful homes on grand promenades. Then the poorer homes were hidden away behind them, and one needed, further, to step inside to get the full impact of the squalor.
Engels blames the horrible conditions of the working poor on the owners of industry exploiting the workers and not paying them a living wage—but, more deeply, he blames these conditions on the capitalist system itself. This was in the early stages of industrialization, and it is true that before the law caught up with circumstances, many poor people had trouble earning enough not to be hungry. Later, minimum wage laws and other legislation would put an earning floor under workers.
Engels calls this underpaying of workers "social murder." One of Engels's points is that the owners may not even know the kind of conditions the working class lives in. He argues that it is the social structure—the way society is (or was) organized to exploit the poor—that leads to this situation.