Hmm..." Arthur pondered Haruko's question. The guy was moving cautiously so he was probably either scared that someone was following him, or he was scared that someone would attack him. Or both. So trying to talk to him could end with violence, while following him might not, but they also risk losing him even though the streets are empty. And there's also a billion other possibilities that Arthur didn't feel like thinking about.
"Right, here's the plan. I'm gonna take Katie and follow him from the sky. You try and talk to him and try and run away if anything happens. We'll help you if you really can't get out, but otherwise we'll stay in the sky since it's better if at least someone can follow him. Or do you have a better plan?"