content: If you don't mind a lay opinion in response to your question, I think it's a matter of having different tools for different jobs. Sometimes it is important to have marked/official-looking vehicles (here is a video I'm basing this on), whereas there are obviously other situations where having a marked vehicle is detrimental to the purpose (surveillance comes to mind). I imagine with this case, it was one of those all-hands-on-deck situations where they weren't picky about marked vs. unmarked. They just wanted to apprehend the suspect.