Well, don't you worry, that's what we call a prologue! And it's not necessary to start off a story like that, you can start wherever you want, really. Hell, you can show the murder as the first thing if you want, but it's important to be intentional with it. Like.. what does it do for your story if you show that scene first, other than using it as hook for readers? Does it come off as cheesy in that "hi, you're probably wondering how we got here" kind of attitude? Do you want it to be ripped directly from a future scene or do you wanna provide a different perspective of what's going on with this intro?
I had a similar concern not too long ago, and people were kind enough to gimme a hand, telling me similar things to what I'm saying now sooo... Hope what I said helps in any way~