In Heat

Directed by John Gallagher
Written by Andi Bushell

Jareau: "There are no secrets better kept than the secrets that everybody guesses." George Bernard Shaw.

Gay men in Miami are targeted by a gay UnSub who was brainwashed by his abusive military father to think gay men deserve to die. One of the victims happens to be the closeted friend of JJ's secret boyfriend, William LaMontagne.

Tropes in this episode

Abusive Parents: The UnSub's father was homophobic and openly trying to beat his son into being heterosexual. It was apparently so bad that the UnSub's sister gave him money so he could escape town.
Armoured Closet Gay: All of the victims were gay. One of them, a friend of Detective LaMontagne, never told anyone at home about his sexuality and even had a fiancée. LaMontagne even wonders why his friend felt like he couldn't tell him.
Author Tract: The episode is basically an excuse to condemn homophobia and the idea of anyone staying in the closet built on the excuse of being about a serial killer. It gets so caught up in it that at one point it delivers a bit of a Broken Aesop when Garcia sneers that a charge of "Public lewdness" must just mean "being gay" in Texas when the Texan in question was shown earlier about to give a blowjob in public.
Big Damn Kiss: At the end of the episode, JJ kisses Detective LaMontagne in full view of anyone, after telling him she does want to be with him. Beforehand, they had broken up because Detective LaMontagne felt like she always had one foot out of the door in the relationship, and he wanted a commitment she wasn't willing to give then.
Double Standard: In the previous episode Hotchner tore Reid a new one for becoming emotionally involved and snapping at people in that case (a bullied young man), but in this episode has no problem with himself and Rossi giving a homophobic father a harsh dressing down. To be fair in this situation there was only two FBI agents in the room as opposed to a full police taskforce in the other episode.
Everybody Knew Already: JJ had been keeping her relationship a secret in part because she hated not having secrets from the rest of the team, but of course being who they are they'd known since the start.
Heteronormative Crusader: The UnSub is motivated by the abuse his homophobic father subjected him to.
I Just Want to Be You: The UnSub imitates the guys he is attracted to because he hates himself and would rather be someone else. He picks up a German tourist and makes him teach him who to pronounce "dangerous" with a German accent. Not "gefärlich", the English word "dangerous", and when they find him, he's speaking English with a strong German accent rather than his native Texan one.
Karma Houdini: We never see Steve's abusive father get arrested for using physical violence against his son.
Real Life Writes the Plot: Will LaMontagne, who first appeared in "Jones" in the previous season, was originally intended to be a one-off character like most local detectives the team works with. However, JJ's actress, A.J. Cook, became pregnant with her first child during the season's production, and rather than attempting a Hide Your Pregnancy, the writers and showrunners decided to incorporate this into the show and have JJ be pregnant as well (which she discovers in the next episode). This meant she needed to be given a steady love interest quickly, and, remembering her Ship Tease with Will in the previous season, he's brought back and revealed to have been in a Secret Relationship with JJ ever since the events of "Jones". He becomes a recurring character for the rest of the series.
"The Reason You Suck" Speech: Hotch and Rossi tear into the UnSub's homophobic father for causing his son to hate himself so much that he's killing other people to take their identity.
David Fitzgerald: I've been a guard for 20 years. I know a little something about disciplining somebody.
David Rossi: So, what, you thought you could beat homosexuality out of him?!
Fitzgerald: I don't like your tone.
Rossi: Threatening this boy with tactics you use on hardened criminals, threatening him with his own life!?
Fitzgerald: I was teaching him how to be a man.
Aaron Hotchner: No, you were teaching him how to kill one.
Rossi: You convinced him he was worthless, contemptible for being who he was. And he believed you, so he found a way to become someone else, anyone else.
Hotchner: Steven isn't missing, sir. He's the offender we're looking for.
Secret Relationship: It turns that JJ and Detective LaMontagne have been seeing each other for about a year, but she has not told the team about it.
Secret Secret-Keeper: The entire team has been aware of JJ's Secret Relationship since the beginning, unbeknownst to JJ.