"They forced our hand. Now, we're gonna have to teach 'em a lesson they'll never forget."
Gulino was a sergeant for the U.S. Air Force and served two tours in the Iraq War. On July 12, 2003, when he returned to the U.S., he joined the Chicago Police Department, getting the badge number of 53699, and was partnered with George Scotman. Both started brutally assaulting suspects to extract confessions out of them. In 2006, a rookie officer named Mark Reyes discovered their illegal activities and filed a report, which then led to an Internal Affairs investigation. On November 13 of the same year, the Chicago Police Department stripped both Gulino and Scotman of their badges. Feeling that he was defined by his badge, Gulino felt wronged by the act and swore revenge against Reyes and the Chicago Police Department, abducting a teenage girl named Stephanie Lawford in 2007 and holding her captive, torturing her into complete loyalty and submission towards him, even possibly being assisted by Scotman, although this is unconfirmed. In November 2008, Scotman died of cancer, and four weeks afterward, Gulino abducted two teenage boys named Brandon Rutherford and Vincent Gamble, torturing them with the intention of brainwashing them and turning them into his own "soldiers". However, when the two rebelled against his method, he used the torture to kill them, disposing their bodies afterwards. On August 2009, he abducted two more boys, Gavin Rossler and Trevor Madison, both of whom were younger than Brandon and Vincent. This time, his method of torture and brainwashing was successful on them. Two years later, Gulino abducted twelve-year-olds Daniel Morrison and Steven Walker, successfully brainwashing the former but being forced to kill the latter after he rebelled.
In "The Return", the seven-year anniversary of Gulino and Scotman being stripped of their badges began to approach. On the day before, Gulino decides to enact his revenge scheme, sending Gavin to a small diner that is frequented by Officer Ryan Clayburn. There, Gavin kills three people, but is shot dead by Clayburn before he can shoot him. The fact that the shooting was carried out by a teenager who had been missing for four years, plus the fact that Trevor dropped Gavin off at the diner, prompts Reyes to call in the BAU to assist the investigation. On November 13, Trevor, acting on Gulino's orders, blocks a sedan in the middle of an intersection as construction goes on nearby and detonates a car bomb, killing himself and a nearby traffic cop. Later, Daniel is tracked down and arrested by Reyes and Morgan when he tries to open fire at a park filled with emergency responders and attending civilians. Gulino is next seen watching a live news report detailing Daniel's arrest, and he observes a clipboard of photos of his abduction victims. The following night, he equips Stephanie with a vest rigged with explosives, a pistol, and a police uniform (the latter two likely his) before sending her over to the Chicago police headquarters to commit a suicide bombing. However, the plan fails when Stephanie is shot and injured by Morgan before she could detonate her suicide vest. With his "soldiers" either dead or arrested, Gulino flees to Scotman's last residence, but is ambushed by Morgan and arrested by Reyes. JJ then opens the trunk of his car and finds a boy he recently abducted, named Cameron Patterson, who briefly identifies himself as another "soldier", but since he is still young, the effects of the torture and brainwashing wears off on him when JJ appeals to him, promising she will bring him back to his parents.
Gulino targeted young Caucasian and African-American children to turn them into his "soldiers". He first abducted Stephanie Lawford, a teenage girl, in order to give the other abduction victims a maternal figure. Then, Gulino abducted young boys, presumably using a ruse of some kind, and held them captive in homemade cages in his home. These boys lived different types of high-risk lifestyles (Brandon Rutherford and Vincent Gamble were street kids, Daniel Morrison and Steven Walker lived in single-parent homes, and Gavin Rossler and Trevor Madison lived in gang territory). These boys were all abducted in pairs in different jurisdictions in Chicago at a 24-hour-long span, initially while fifteen years old, but then Gulino progressively began abducting younger victims so then they could cooperate more easily.
He would torture them using methods originating in the Vietnam War, which involved firing blanks from a handgun into their temples while they were blindfolded and tied to chairs, and also twisting their arms until they broke. Initially, the torture was much more severe and resulted in the deaths of three of the boys when they rebelled, but the magnitude of the torture eventually lessened, allowing for more effectiveness. After killing the boys who rebelled, he dumped their bodies in random areas of Chicago. For some reason, he always took photos of the victims he abducted and put them up on a clipboard.
Gulino also brainwashed them, effectively turning them into killers that were loyal to him, followed his orders, and would not say anything useful if they were captured. He programmed them to only say their names, the fact that they were his "soldiers", and his badge number. Once that was secured, he would send them out to attack locations connected to the Chicago Police Department in order to get revenge on them. While the small diner regularly frequented by an officer was of minor significance, the attacks grew in severity and occurred in larger locations, such as street intersections and parks where officers patrolled.
"Everything we worked for, all these years... It's come to this moment. Make me proud."
The unsub is the leader of a homegrown terrorist organization, and also a preferential offender targeting and abducting prepubescent boys, who is likely a male in his 40s with some military or law-enforcement training. He has a secluded location that provides enough privacy to hold his victims captive for several years. During that time, he breaks the children down psychologically and rebuilds them as hardened soldiers who follow his orders. The children are suffering extreme cases of Stockholm syndrome, as he is instilling the feeling that he is their only family and that the rest of the world are their enemies. He uses military-style torture techniques in order to get his victims to see his enemies as their own, including putting them through a rather rigorous and punishing military training regimen in order to prepare them mentally and physically for his personal war. When that happens, the physical threat stops and the reprogramming begins. Once he has their trust, he maintains his connection to them by bolstering them with love and affection. His connection to the children is important, for it ensures that once they are released, they will not deviate from their given orders. While his ultimate target has not yet been determined, it could be as broad as average American citizens. The attacks have been well-orchestrated, methodical, and violent, definite signs that they are meant to maximize destruction and panic, which makes it important for authorities to get ahead of him, but for that to happen, the source of the unsub's rage must be identified first.
The aspect of Gulino's M.O. that involved abducting children and keeping them for several years, during which they were brainwashed into obedience to the point of staying with him, seems to have been based on Robert Berchtold, a pedophile who abducted twelve-year-old Jan Broberg at around 1974. Broberg, who has since become an actress, also appears in the episode, starring as Lauren Morrison, the mother of Daniel Morrison, one of Gulino's abduction victims who was successfully brainwashed into loyalty and obedience; this was most likely a reference to her childhood abduction.
The scenario of Gulino abducting boys, turning them into his own personal army, and using them to commit a spree of shootings and bombings also sounds reminiscent of an aspect of an original plan for the Beltway shootings, as confessed by Lee Boyd Malvo. This plan involved him and his partner John Allen Muhammad recruiting orphaned boys, training them in the usage of firearms and stealth, and using them to commit shooting sprees in Canada.
In addition, Gulino's scheme to get revenge against the Chicago Police Department may have been directly or indirectly inspired by homegrown terrorist and spree killer Christopher Dorner, who was also a wound collector. Like Gulino, Dorner formerly served in the U.S. Armed Forces (in his case, the U.S. Navy Reserve) before being discharged, to which he then became an officer for the Los Angeles Police Department before his employment was terminated after allegations of him assaulting the suspect of a disturbance case were made. Dorner's partner was also involved in the case, although her outcome was completely different than that of George Scotman's. This termination of his employment would prompt Dorner to commit a week-long killing spree targeting mostly police officers, under the belief that he was framed and that the allegations were founded purely by racism. The major difference between Gulino and Dorner was that Gulino sent others to attack the Chicago Police Department and had them target random civilians as well, while Dorner directly committed his killings and had specific targets.
Gulino is also similar to Jon Burge and may have been based on him, at least partially. Both served in the U.S. Armed Forces and were honorably discharged, joined the Chicago Police Department afterwards, and were fired after it was learned that they would abuse suspects to get confessions out of them, with the number of victims ranging in the dozens.