Context: I'm a professional writer. Specifically, a journalist for an online tech news publication, which means there often isn't time to nurse a block.
Life circumstances can and have impacted my ability to write, but what has worked like clockwork for me every time is to just sit down and write.
Write your opening sentence and if you don't like it delete it, or better yet go to the front of it, hit enter twice, go back up to the top of your page and write a new one.
Repeat until you either have something workable or more than five minutes have passed, and then continue writing.
At the end of this you might have something that isn't very good, but from there you can rewrite and refine. It might take you a bit longer to write something than you're used to, but you will have written it, block or not.
One last thing: author John Green says a thing (which he used in his novel The Fault in Our Stars) which I agree with — Pain demands to be felt.
If the robbery is dominating your thoughts, then write about that. Get it out of your head and onto the screen. Even if you never publish it.
RE: Writer´s block - How do you deal with it?