Ava and Nate are in a tailspin with the dead body of someone they know literally placed on their doorstep by Matt, and while he does have a compulsion to kill and in his mind killing is for the good of the podcast in the direction he sees it going with or without Ava and Nate, Matt believes he did have good reason for killing this time. Leaving the body with Ava and Nate is arguably to demonstrate to them that he is the one in control regardless of what they may believe. Disposing of the body, while already difficult for Ava and Nate, is made even more difficult in the position Matt places them in in they needing to show their friends that everything is normal in their lives. The one upside may be they coming together to deal with the situation as husband and wife, especially important in they imminently becoming parents for the first time.
—Huggo