In my estimation, Brendan had many things wrong. Laura knew the baby was Brendan’s, but told Emily to tell Tug it was his. She didn’t do this to get Emily killed. She did it to get Emily away from Brendan, whom she had always wanted.

At the beginning of the film Emily tells Brendan on the phone, “I did what she said with the brick.” Brendan figures the “she” is Laura, but it’s more likely Cara, who is a competitor of the Pin, and jealous of Emily’s relationship with Dode. It’s Cara who puts Dode in front of the gun, after all.

Tug killed Emily because she told him she was pregnant and that the baby was his and because he’s a really lousy guy.

Tug killed Dode because he thought Dode was about to put the finger on him for killing Emily, which of course made his guilt obvious to everyone, and soured his reputation with the Pin.

Now to Brendan. Brendan has shit wrong. He’s blinded by his feelings for Emily that he can’t see that she’s a junkie who sleeps around. So he remembers what Emily said during the opening scene phone call: “I did what she said with the brick.” After everything and finding the arrow on Laura’s cigarette, Brendan is certain that Laura “put her in front of the gun.” So Brendan put Emily’s body in Tug’s trunk, wrapped in black garbage bags. The garbage bags reminded him of the brick (it was also wrapped in a garbage bag), so he stole it and put it in Laura’s locker.

Laura had always wanted Brendan, since long before this story started. When she encouraged Emily to tell Tug about the baby, it was selfish, not because she wanted Emily dead, but because she wanted Brendan for herself. Truth is, Brendan was the one who put Emily in front of the gun, by pushing her away when he gave up his partner Jere. And now he’s framed Laura, who he pegged as a femme fatale, but turned out to be the real damsel in distress. Remember, she begged Brendan not to go to the meeting or to the Pin’s house. She wanted him to go to the hospital. At the end Laura doesn’t admit guilt, or maybe she did feel guilty for sending Emily to Tug. But she lets Brendan know a few other things; That the baby was his, that she took Emily to the doctor, etc. It’s possible that she didn’t know that Tug had killed Emily until this point.

So who encouraged Emily to recut the brick? Probably Kara. Dode was her man and he was stepping out with Laura, who he thought was carrying his baby. Kara set up Emily. Then she set up Dode.