"He killed my daughter! He killed Megan!"
Little details are known about Larry's life prior to "Brothers Hotchner", other than he worked as a baggage handler at Franklin Airport and that he apparently has a good amount of experience with drugs. On March 16, 2013, his daughter Megan died in a bar called the Obsidian, and the death was written up as an apparent ecstasy overdose. Unconvinced, he blamed a man named Jim Peters, who owned the Obsidian, and formulated a revenge scheme to get back at him by targeting a bar he owned and poison unsuspecting customers, presumably to attract bad business for Peters' venues. Knowing that the authorities would trace a potential attack back to him, Larry ignored the Obsidian and targeted another bar owned by Peters called the Edinburgh, which coincidentally employed Sean Hotchner, the brother of SSA Aaron Hotchner.
After killing a fellow baggage handler named Mike Spires, who was also a courier for drug dealers, Larry assumed his identity and began importing a powerful drug known as PMMA, infamously nicknamed as "Doctor Death" due to its lethal nature upon being used frequently. He mixed the PMMA with methamphetamine and left it at several drop-off points for drug dealers, who assumed it was liquid ecstasy and sold it to customers. The drug took its effect on four people that went to the Edinburgh, including Sean's girlfriend Linda Heiying. What Larry didn't realize is that Peters and his employees spiked their white wine with his drug as a prank, not knowing about its lethal effects.
When a fifth victim, a barfly named Anna Johnson, dies in front of Sean and the manager, the former calls in Hotch for assistance, as he is suspicious of her death when it is viewed as an ecstasy overdose, and also when the manager was hesitant to call 911 even after Anna died. Meanwhile, Larry goes on a killing spree, claiming six victims celebrating at a rave party, including a man who received the drugs and supplied it to the other victims. Shortly afterward, a couple dies in front of their daughter after drinking white wine spiked by Peters. Finally gaining enough confidence from his killings, and also angered towards him over the couple's deaths, Larry attacks Peters directly, smashing his car into his at a parking lot. Then, he kills Peters by forcing PMMA down his nose and throat and then leaving him to die. Eventually, Garcia tracks down the record trail left by Larry in Spires's name. The BAU eventually identify Larry as the unsub and track him down to Franklin Airport. There, Morgan and Reid confront him; he pushes a cart at the former and makes a run for it. However, Reid instantly subdues him, and Larry is arrested. As he is taken away, he starts ranting that Peters killed his daughter.
Larry's victims would all be killed by overdosing on PMMA, which would cause their internal temperature to rise to a point where they were literally boiling from the inside-out. As a result, they would bleed out severely from their mouth, nose, ears, and even eyes before dying. He would have the PMMA imported from Canada to his workplace and then mix it with methamphetamine to make it appear as having the same effects as liquid ecstasy and to dilute the effects of the PMMA so the victims would want to take more of it, ensuring their deaths. He would then place it in vials and leave it at multiple drop-off points (excluding one where the drugs would be routed to the Obsidian, the same bar where his daughter died, as part of a forensic countermeasure), where it would be picked up by drug dealers who would then sell it to local clubs such as the Edinburgh, one of the clubs Jim Peters owned, and underground party venues. While one victim was initially killed at a time by the PMMA they bought from the dealers, multiple victims would later be killed at once, like a large group of people celebrating at a rave party. Some of the victims weren't killed at the bar, instead being poisoned by white wine delivered by the bar, which had been spiked by Peters and his accomplices.
When he attacked Jim Peters, he subdued him by crashing his SUV into his car, and then personally killed him by forcing PMMA down his nose and throat. Considering that he wasn't equipped with poison at the time of his first murder, it is unknown as to how he killed Mike Spires, although considering his death was written up as a car accident, it is possible he killed him using a vehicle.
The unsub is a sociopath who is poisoning his victims with a drug known as PMMA (also known by its street name of "Dr. Death") and may be altering the drug to make it more lethal to everyone who uses it. He gets off on the spectacle, and to him, it is not just about the victims; it is about the witnesses. His goal is to incite fear, meaning that he is very desperate for attention, and that he wants all eyes on his work because he craves recognition. He will be paying close attention to the media, allowing him to relive the crimes. He uses a drug known for its euphoric effect, as if like he wants to take happiness away from his victims. He is taking the law into his own hands by killing known drug users. The rave party massacre means the unsub is trying to make some form of statement. He wants to increase his body count and doesn't care who he kills (this later proved to be false as the unsub did not mean to kill Bernard and Catherine Hatchitt).
The murder of his recent victim Jim Peters is personal and indicates that he is no longer content to sit back and watch as his victims die. He may also have had a grudge against Peters for some reason; he may hold Peters responsible for Thane Parks dosing the Edinburgh's supply of wine, as that was not his intent and may even target other employees of the Edinburgh. The unsub killed Mike Spires as a way of getting access to the drug supply and may be a baggage handler like Spires, as they are paid to keep quiet when giving the drugs they import to dealers. He may have also suffered a drug-related death in his family.
Larry's killings seem to be based of the paraquat murders, a series of murders that occurred in Japan in 1985, in which people were poisoned by drinks containing pesticides that were in or around vending machines. In both cases, the victims were killed by beverages laced with poisons and the body counts were in the double-digits.
- April 26: Mike Spires (killed by unknown causes for access to the drug supply; his death was written up as a traffic accident)
- May 15-21:
- Jason Purgas
- Linda Heying (Sean Hotchner's girlfriend; unintentionally killed)
- Richard Burog
- Erik Sullivan (unintentionally killed)
- May 22: Anna Johnson (unintentionally killed)
- May 22-23: Six killed in the rave party massacre, including the drug supplier. They are:
- Jason Pampas
- Janet Lamore
- Charlotte Dovson
- Richard Kutzig
- Connors McCarty
- May 23: Bernard and Catherine Hatchitt (both unintentionally killed)
- May 24: Jim Peters (subdued by a car crash, forced PMMA down his nose and throat, and left for dead)
- Larry bears similarities with Patrick Meyers, a budding spree killer who appeared in Season Five. Both were fathers who lost their children in an accident of some sort and both attacked whom they believed was responsible. However, Larry succeeded in killing his target, whereas Patrick wasn't as successful.
- Larry is one of few serial killers on the show to successfully kill all of the victims he targeted. The others are Steven Fitzgerald, Megan Kane, Vincent Rowlings, Lee Mullens, Paul Westin, and Charles Johnson. This is a very rare occurrence, as the serial killers depicted on the show typically have at least one survivor.