NBC's "Chicago Fire" returns in the fall for a fourth season in which fans will figure out what really happened to Casey (Jesse Spencer).

In the Season 3 finale, Dawson (Monica Raymund) had taken a mystery pregnancy test. While the results were not shown, she rushed to Casey's to give him the news, but he was nowhere to be found. Instead, Dawson found a dead stripper at Casey's home.

The stripper, Katya (Izabella Miko), was from a club where Casey was doing construction. According to TVLine, the shady club owner Jack Nesbitt (Eric Mabius) might be responsible for the murder. He was known in the show as a human trafficker as well and may have been out to get her.

But where is Casey? And is Dawson actually pregnant?

The way she rushed over to Casey's hints that she is pregnant. And if she is, will she be a single mother? It is not clear if Casey was murdered to keep quiet, or kidnapped after Nesbitt found out that he was working undercover.

Showrunner Matt Olmstead tells TVLine that he is leaving the idea of what happened to Casey open. He could have been framed for the stripper's murder or he could have been kidnapped.

"Maybe both," Olmstead said. "We left it open, and we have a couple ideas on the board -- a combination of that or one of [those]."

Meanwhile, fans do know that Katya was over Casey's house for business and not romance despite speculation that they were romantically involved.

"There was [connection between Casey and Katya]," Olmstead revealed. "We wanted to play a little flirtation more so on her part, but we never fully wanted to go down that road."

Meanwhile, Olmstead hints that Katya could have tried to save Casey. "Her being forced to go there and try to lure him out is a possibility," he said.

"Chicago Fire" returns to NBC on Oct. 13.