In the season 1 pilot, Carrie gets a folder from Al, with a simple note: "I never gave up." It's everything ever collected on the case of her sister's death.
In "Manhunt", Shawn Manning, proven innocent, is offered a job by the woman he was initially accused of raping.
In "Till Death", A prostitute talks about how the men she sees never seem interested at all in their wives, but Al, who isn't married to Carrie, can just say a few things about her and she can tell he still loves her.
In "Stray Bullet", Elliot being willing to look the other way while Carrie tracks down who framed Al, as well as the whole team welcoming back Al after he is cleared of murder.
In "Throwing Shade", Carrie helping Elliot with getting a witness to put him at a different spot on a particular date so his ex-friend Bright can't try to deep-six his career. In addition, Elliot's start of reconciliation with his wife, Shelby.