Chicago Fire and Chicago PD crossover: Who killed Shay? Watch episode 13 'Three Bells' live stream online

Chicago Fire season 3 will return with episode 13 titled, 'Three Bells' which will focus on Shay's murder investigation and the future of Casey and Dawson's romance.

In order to investigate the case, Firehouse 51 will seek the help of Chicago PD and the crossover episode will run for two consecutive days, Tuesday and Wednesday.

Click here to watch the crossover episode live stream online.

Click here to watch the previous episodes of the popular NBC series online.

In the previous episode, Severide and Dawson look into the Storage Building fire which killed Shay last year.

The episode aims at discovering the murderer and his murder motive.

"This was a murder. This wasn't just an accidental fire that was set," executive producer Matt Olmstead told TV Line.

"It becomes about narrowing down who set it. Arson is difficult to prove, so it's not a slam dunk thing of getting fingerprints and a confession."

He also teased that the case will put the entire team at serious risk.

"There's some finesse involved and patience and risk in trying to get the suspect in the act or putting him in a place of discomfort where he might act out. It's a roll of the dice. On Fire, [it's about] the awareness this might happen and the identification of the suspect, and then the hand-off to P.D.: How are they going to actually arrest this guy when he's proven to be fairly wily?"

Olmstead also revealed that the future of Casey and Dawson remain unsure.

"They've been through enough and are wary enough that it doesn't all of a sudden swing the pendulum all the way back toward a relationship, because then they're going whichever way the wind is blowing that day. So it definitely affects him seeing her in danger, but they're at a place right now that's fairly firm in terms of where they're at and cooling it off."

He also teased that there will be new love interests for them in the upcoming episode as "They're both trying to get out of the block, so to speak, but nothing profound yet."

Chicago Fire season 3 airs every Tuesday night on NBC.