It was a fine day to make trouble. Jin and, say, one hundred clones of his (albeit, he couldn't pull that off yet) would all much agree with this say and perhaps even make it a consensus. He was let into the underground by a few of the people, all of whom were special guards assigned to this role by the government official who resided within the subterranean settlement himself.
Luckily, Jin was seen as Johnson as he walked across the underground pathways, and only because of this was he let into the base, to begin with. He had micmicked Johnson's form with the help of his shapeshifting skill of which he was now thoroughly content.
It was indeed a useful skill that could get quite helpful in dire times and consequences. What's more, maintaining the form of another person took much less energy compared to invisibility. He could have retained a stolen form for days.
