I actually had zero fincrime experience when I applied for the job! I applied because I thought I had some skills which fit the job description (I’d previously had jobs that had a customer-facing element, I love solving problems and investigation/analysis, etc.)… but probably the main reason I applied was because in the first job I got when I moved to London, my new employers (who never paid me) turned out to be fraudsters. That’s a whole other story though 
This is such a cliché, but genuinely I found that no two days were the same, probably because fraudsters are pretty good at switching up their methods. The range of financial crime we’d come across meant that we were dealing with things that we came to consider ‘common’ behaviour (like stolen card fraud), to situations that were completely bizarre or difficult to untangle. I’d really recommend reading the Q&A done by Shak (a current Fincrime Spec) a few weeks ago if you’re interested in finding out more about the job: Monzo Staff Weekly Q&A - Shak Welch (COps, Financial Crime Specialist) - #27 by SHAK