Well, so Julia is improbable. Julia is/acts also a bit erratic, however. But it could also be that Julia planted them, and the grunt detonated those. It is assumed this was a one-man's job, but what if it wasn't? The grunt could be tasked by getting close enough, then detonate it, without knowing who in their team planted the explosives. The only thing is, I don't really know if Julia would or would not be suspected if she was there in the train station before you came there. She's a gym leader, but she also likes to blow things up, so idk if this could be possible...