If Kieran felt Barney the "Jackal" wasn't simple before, he was certain that Barney wasn't who he claimed to be after seeing the hidden entrance with the wooden cupboard blocking it.
A street thug who was a drug addict could easily move a solid wood cupboard that required three to four people to move?
What a bad joke!
Was there someone else who helped him instead?
Well anyone would want his secret entrance to be kept away from other people's reach.
It was common sense!
Therefore, Barney the "Jackal" was not someone to be underestimated in terms of strength.
Still, despite him purposely concealing his strength, he was taken out easily by that assailant.
Based on the traces on the scene, Kieran believed that Barney was taken down before he even had the chance to resist and began that long interrogation session.