This theory is in support of my previous theory here: http://www.whoisredjohn.com/See-a-theory-Red-John/7165

Notice that in the last episode, before Reede Smith killed Kirkland, when Kirkland was moving out of the van he did some sort of swallowing act. Forensics investigating his death will reveal whats in his body in the next episode.

There are two possibilities here (if he really swallowed something, wasn't his natural acting though):

1. He swallowed something that will leave a clue for Jane to find Red John/Tyger Tyger organization

2. He swallowed the instant death pill criminals use to kill themselves - This will prove that Kirkland didn't plan to run from the van as he was to kill himself through the pill. Hence, proving that he was murdered.

Jane will come to know that Kirkland new something big...we'll know in the next episode if Jane will come to know about this 'Tyger Tyger' organization or not.