Depiction of the Crossed
The Crossed themselves show considerable variation, as they are still self-aware individuals, albeit turned into homicidal maniacs. The actual level of insanity different Crossed demonstrate ranges across a wide spectrum as well. Many are practically feral savages with absolutely no regard for their own self-preservation, to the point that they will gleefully mutilate themselves for the sheer thrill of it, including amputating their own limbs (understandably, these Crossed don't tend to survive very long). Most are capable of basic albeit deranged speech and wield whatever clubs, knives, or sharp objects are at hand to attack anything around them. The more insane Crossed will even attack each other, though they apparently prefer the non-Crossed. Some characters speculate that this preference is due to their need for sadistic gratification: given that the Crossed are so insane that they will mutilate themselves voluntarily, it isn't as fun to torture fellow Crossed as it is to torture uninfected, frightened victims.
The Crossed enjoy artfully mutilating the bodies of their victims, amputating limbs or worse. The Crossed can survive on any food but frequently rely on basic cannibalism – not because they have a zombie-like need for human flesh, they're just so brutal and cruel that they get warped enjoyment out of it. Moreover, as years pass after the outbreak and the normal food sources of civilization disappear, other Crossed increasingly cannibalize the non-infected or each other to survive.
The Crossed are consumed by a pervasive bloodlust and constantly try to rape anyone or anything they can chase down. The infection spreads through bodily fluids, thus anyone raped by a Crossed will become a Crossed themselves, provided that their attackers don't kill them before they turn (which they frequently do). This is just a matter of preference, however, as other Crossed will kill their victims first and then rape their corpses. Still, it is more common for them to rape live victims, because they enjoy causing their victims to suffer through slow torture instead of giving them a quick death. A major way the infection spread in the first hours and days of the outbreak was when in a veritable blood orgy, the Crossed would rape and sodomize entire families and neighborhoods, rapidly expanding the growing hordes of Crossed. Many of these rapes aren't consciously intended to infect other people, it simply occurs as a byproduct of their insatiable need for violence. Female crossed will also try to violently rape and sodomize people with whatever tools or weapons are at hand. On rare occasion, pregnant women who have been infected and turned survive long enough to give birth, but their babies are born infected as well - apparently the placental barrier provides no protection against the infection (though it is possible that it does, but unsanitary birth conditions infect them during delivery itself, like Neonatal conjunctivitis). Crossed women who have given birth are, however, gleefully willing to needlessly murder their own newborn babies.
The mental effects of the Crossed infection are apparently not just a zombie-like drive for basic desires like violence and sexual gratification. It seems to give the Crossed a driving need to perform actions which they perceive as morally bad, somehow triggering the parts of their brains which control their darkest, subconsciously pent-up inhibitions. The Crossed do not simply rape and kill their victims, they torture and mutilate them to cause the maximum amount of pain and suffering. Another symptom of this is that they tend to attack and deface things and places which are considered particularly sacrosanct, i.e. defacing government buildings with corpses, or desecrating religious buildings. Crossed who manage to capture a non-infected human on a scouting expedition from a survivor enclave will frequently proceed to torture and mutilate their captive within sight of the survivors' fortress, to inflict psychological torment on the unreachable people inside.
At the other extreme, however, some Crossed have been shown to be quite capable of complex pre-meditated actions. Not consumed by unthinking bloodlust to the extent that many of the other infected are, they have enough mental where-withal to plan ambushes and traps, and organize gangs of Crossed to assault survivor enclaves. The more mindless rage-consumed Crossed will still know how to use firearms if they find them but usually won't think rationally enough to plan out where to acquire more firearms. The more rational and calculating Crossed, in contrast, will actively seek out armories to acquire new firearms. Some of these more rational Crossed will self-consciously coat their weapons in their own bodily fluids, actively trying to turn non-infected survivors into more Crossed. These are generally seen some time after the outbreak: Shaky's theory in "Wish You Were Here" is that this isn't something so complex as the Crossed "evolving", but that a process of natural selection set in: after several years, the Crossed who were too insane to look after themselves died out (Badlands #3 shows Crossed dropping dead in winter because they didn't think to wear clothes), while the more calculating ones took steps to survive.
The three most prominent Crossed characters focused on were Horsecock in the original series and Smokey in "The Quisling", who the protagonists had to take out to stop their gangs from spreading, and the nun Aoileann in "Wish You Were Here". In comics by Simon Spurrier, this is attributed to some quality in the infected or their circumstances before infection: Shaky says that Aoileann is good at "holding back passion" (which is mistaken for control) and simply passed this on to her group, Russian gangster Mattias had periods of control (followed by violent mania) due to brain damage from long-term ketamin use, and an Australian was focused on getting revenge. In "Wish You Were Here", it is vaguely implied that Aoileann's unusual reaction to the Crossed infection may also be due to her having Epilepsy, altering how it affected her brain. Aoileann is capable of having lucid conversations with other people, making complex future plans and traps, and even seems to have retained certain empathetic emotions, as she is actually horrified at the prospect of personally killing other people (though she lets her followers kill uninfected people).
A curious point noted by several characters is that even since the earliest days of the outbreak, some survivors have attempted to slip past the Crossed by painting red cross-marks on their faces to simulate the rashes from the infection – the Crossed will attack other Crossed if they're bored or frustrated, but at least some of the time will leave other Crossed alone. However, it does not matter how accurate the reproduction of the rash-marks are, even with high-grade makeup that makes them visually identical to the real rashes, the Crossed are somehow always able to tell that it's a fake. As characters note in The Fatal Englishman, having survived five years since the initial outbreak, they have never seen this trick succeed; somehow the Crossed are still able to detect the non-infected.
When the infection first started, the victims may have been homicidal, suicidal, or simply dropped dead; some showed grief about what they were doing. Within a few days, the first cross mark had appeared and this became the standard outcome.
Before The Thin Red Line, the Crossed stories agreed that the infection was stunningly rapid, so fast that the news media and most world governments had little if any time to respond, but the exact specifics of the outbreak differed from writer to writer. Depending on the story, it took anywhere from a week to a mere matter of hours for the infection to spread across the globe. In the original story, the infection erupts suddenly across the entire United States without warning and later spreads; a survivor says Canada tried to fortify the border "in the first week" and were unaware the virus had reached them until after that point. In contrast, Badlands #14–18, #40-43 and Wish You Were Here have the infection erupted across the entire planet in the same day, the latter two showing United Kingdom and Japan being rapidly overrun; Badlands #16 has the White House (and Surgeon General) and part of the news media still around the next day, reporting on the crisis. Badlands #10–13 ignores this and has the Crossed tearing through small towns without being noticed, getting more and more numerous over the course of a week; and Badlands #26, also by Ennis, has a British soldier named Harry (later appearing in The Thin Red Line) say he's been aware of the Crossed for "the past three days" by the time the outbreak is public.
In the stories where the infection is sudden, the Crossed as shown overrunning the United States at sunset/night and London in the afternoon, meaning one nation had to be overrun before the other. In Ennis' first story, survivors find the journal of a soldier who theorized that there was no single point of origin and it may have been a strategically triggered bioterrorist attack which was simultaneously released at multiple points around the world.
The Thin Red Line (Badlands #50-56) finally established an origin and timeline of the infection. (The origin would, however, clash with other outbreak stories: London is not overrun for several days, the White House is overrun before most of the US, and the Crossed are public before an outbreak in Japan or most of the US)
The outbreak began in summer 2008 in Yorkshire, United Kingdom (the time of the first comic): the patient zero was a man who had a psychotic breakdown and murdered his family, and the infection spread rapidly from two local policemen to the entire population of the village of Tethersby. Indecisiveness by Prime Minister Gordon Brown meant that a state of emergency wasn't declared until after a Sky News team found and filmed the villagers committing a mass suicide. From this point the infection spread rapidly, and the Prime Minister and his staff were moved into a secure bunker guarded by the SAS and SO1 police officers which also doubled as a medical research centre where "Patient Zero" was placed under quarantine.
Later in the day, Crossed had overrun most of Yorkshire and other parts of northern England and Scotland, with smaller outbreaks appearing further south. Under the belated state of emergency, the UK suspended all public transport, airlifted troops back from Afghanistan, and blockaded the M1 motorway just north of Northampton; south of there, cordons held and prevented large-scale refugee migration (which could bring more of the infected south). By the evening there were reports of infections in France, Chad, Australia, South Africa, Pakistan, Russia, and the United States. Pakistani Crossed dropped a nuclear bomb on Delhi and Prime Minister Vladimir Putin requested the RAF shoot down 40 Crossed-piloted Tu-95 bombers before NORAD - unable to launch planes due to similar problems - feel obliged to launch nukes. When Gordon Brown contacts the White House, the person answering (implied to be President George W Bush) is clearly infected, confirming Washington D.C. has been overrun and that the American government has fallen. A single Tornado GR1 was launched to intercept the Russians and the crew sacrifice themselves to prevent nuclear war break out. Around this time, while the UK government has failed to stop misinformation and panic spreading on social media, it's clear that the infection is being contained and it might be possible to save the island. (The Ministry of Defence requests to abandon Whitehall as a precaution but are rebuffed by a more determined PM, who insists that they stay so as not to panic the populace) A few hours later, these orders are changed: the government is evacuated to bunkers and orders go out to shut down all nuclear facilities. However, Brown says in the long term they should "hopefully" regain control and that government scientist Dr Chopra has a chance of finding an answer to the virus.
Unfortunately, Brown's advisor - acting without clearing it with the PM - had ordered two of the SAS to torture "patient zero" for information. Under the beating, the individual calmed down, became hostile, and infected the soldiers. Before anyone is aware, Dr Chopra is infected, attacks the Prime Minister, and the bunker is either slaughtered or infected. Harry escapes, taking only the codes for Porton Down: ordered as a last resort to release the deadly biological and chemical agents stored there to wipe out the Crossed, thus giving humanity a chance to fight back.
During the story, Chopra pointed out that the British "patient zero" cannot logically be a patient zero if the infection is appearing so far abroad, and theorises if the virus is "something in the D.N.A.... the planet's" that has manifested and this is why it doesn't follow any known scientific laws. 'Patient Zero' himself was aware of events he could not possibly have seen or heard and saw visions of atrocities he was unaware of, suggesting a paranormal angle, and refers to it as something that "cleanses".