Social isolation suggested as common, crucial risk factor of mass violence
During rush hour on Friday Dec. 19, 2025, a man conducted a mass killing spree at Taipei Main Station exit and at a department store next to MRT Zhongshan Station. He killed three and injured 11. The attacker died immediately after jumping off the building. Cases of mass violence may be relatively rare in Taiwan, but they’re worrying all the same. More so, because they indicate larger societal and structural risk factors that played a part in driving the attackers to violence. So what exactly is the socio-psychological root of mass violence? Let’s find out now in our Special Report.
In 2021, on the night of Halloween, screams erupted on a Keiō Railway train in Tokyo, Japan. A man dressed up as a clown conducted mass stabbing of fellow passengers, and arson. A total of 18 were injured.
Earlier, in 2014, another stabbing spree took place outside a subway station in Chiba Prefecture. The perpetrator attacked four passers-by, leaving one injured and another dead.
Since the 1990s when Japan began formally documenting statistics of mass killing events, at least one would occur every year. There were 14 such cases in 2008 alone.
The most chilling of all was the 2008 Akihabara massacre. The perpetrator drove a mini-truck and rammed through the pedestrian area. Then he exited the vehicle and began stabbing. Within five minutes, he killed seven and injured 10.
Witness
2008 Akihabara massacre
The mini-truck ran over three people. It didn’t look like an accident. It ran over about three people in high speed.
The perpetrator of the 2008 Akihabara massacre was a 25-year-old contract worker. His dissatisfaction with employment and personal life drove him to violence.
Tai Shen-feng
Professor of Criminology, CCU
The perpetrator in this case was unhappy that full-time employees had their own desks and lounge, while contractors like him had to squat in a corner or gather in a separate space to eat their bentos. It’s this feeling of differential treatment that made him feel marginalized very deeply. The last thing that happened to him was when he couldn’t find his work gear. Someone left it in the restroom. That’s a rather extreme example of social rejection, which aggravated him. He likely thought, “since society doesn’t care about me, what’s wrong with me annihilating others?”
In Taiwan, such cases of indiscriminate killing, in which victims were targeted at random, gained widespread attention in 2012, following a brutal case of child murder at a game arcade.
Tai Shen-feng
Professor of Criminology, CCU
“Indiscriminate” here is a direct Japanese loan word. Of course it differs from our concept. It’s not really indiscriminate. Someone will have to get close enough to get killed. Taiwan has very strict gun control, so it’s not possible to do this from a distance. Rather, it’s a form of mass murder in a very short period, causing a great number of casualties in a very short period.
Call it indiscriminate killing, random killing or more accurately, mass murder, this form of homicide are all characterized by a stranger relationship between the perpetrator and victims. Anyone in a public space could be randomly attacked.
Hsu Fu-sheng
Central Police University dean
Think about it. You happen to be walking down the street only to get stabbed and killed by a complete stranger. That sense of fear. I believe anyone would be frightened. That’s why random killings or indiscriminate killings cause such great terror.
On the afternoon of May 21, 2014, a stabbing spree erupted on the Taipei MRT’s Blue Line. The attacker was quickly captured at Jiangzicui Station by the police and members of the public, but he still caused four deaths and 24 injured. Shock and fear quickly rippled through society at the wake of the incident.
Little by little, people in Taipei dropped their guards. But exactly ten years later, on the same day in 2024, a similar knife attack took place on the Taichung MRT.
Fortunately, no one lost their lives this time, thanks to brave passengers. But very soon, on Dec. 19 the following year, Taipei MRT was again the site of violent crime.
Tai Shen-feng
Professor of Criminology, CCU
The way the crime was carried out this time around at the Taipei MRT was even more sophisticated. He had exhibitive props, such as the addition of smoke bombs, which he used in an attempt to create terror. He killed those who stood in the way of his criminal plan, those who he perceived as obstructions. We can reasonably deduce that the perpetrator thought those he killed were those who obstructed him from taking the next steps. For example, sometime stopped him from lighting up the Molokov cocktail, or maybe someone caused him the trouble of having to go through traffic before he could enter the store. His killings were done to eliminate those obstructions.
This time around, the perpetrator killed three pedestrians and injured 11 within three hours. He also died after jumping off a building during a police chase. All three instances of mass attacks on the metro were astoundingly similar in execution.
Hsu Fu-sheng
Central Police University dean
The commonalities, I guess, are that all of them chose public spaces, targeted complete strangers and instilled widespread fear and panic. The perpetrators often choose highly visible public places, train station and the metro are typical examples. The action must be shocking, and it was especially so this time around. The key is to instill fear in everyone.
Sadness, fear and rage were in everyone’s heart after the tragedy, but also questions. Why did all three attackers target strangers without any regard?
Hsu Fu-shen
Central Police University dean
Speaking of the perpetrator Cheng, he did well in high school, at Banqiao Senior High. He later attended the National Defense University but got expelled, and then he transferred to Tunghai University, and became interested in killing others. It’s worth noting these shifts. It’s the same with Chang in the recent incident. He also did well in high school and university, but he experienced a major setback when he was dismissed from the military after being caught drunk-driving. And he only stayed on his next job as a security guard for a year. In the year or so afterwards, he started planning the mass murder. What was the impetus? At which point was he completely abandoned by our society and its systems and institutions, which in turn motivated him to commit this form of lone actor terror?
Only the perpetrators themselves can fully explain their motivation. But Cheng of the 2014 attacks was executed in 2016, while Chang of 2025 plunged to death immediately. Only the Taichung MRT attacker, sentenced to nine years and nine months in prison, could serve as a research subject.
Tai Shen-feng
Professor of Criminology, CCU
In the Taichung MRT incident, the attacker survives. After analyzing lots of data, we discovered that the attacker had trouble adapting in new stages of life. He experienced difficulties at home and in school. He felt bullied in school. The attack was his way of avenging, which he saw as an exercise of justice. He sought justice, alright, but the method wasn’t ideal.
Chuang Yueh-hsiang
Flying Youth mentor
We’d describe this as the safety net in their heart fraying bit by bit. Once they lose their family, friends, colleagues, work, their support system would come undone little by little. Imagine that every individual is a web within a larger system. If every link snaps, the individual’s life is no longer supported. When someone becomes isolated to a certain extent, they become negative. When these negative thoughts accumulate, they’re expressed in harmful action, whether to the self or to others.
Researchers believe that instigators of mass murder at home were similarly motivated as those in Europe or Japan. They’ve all experienced, or rather perceived, great social rejection.
Tai Shen-feng
Professor of Criminology, CCU
What’s perceived social rejection? It’s when an individual believes that people around them are marginalizing them, despite otherwise. It’s a form of cognitive distortion. The individual may perceive others as targeting them in some way. That perception would aggravate feelings of hostility, and the intensification of such feelings could motivate the individual toward aggression.
In all three cases, the perpetrators were in their twenties, transitioning from campus life to the job market. It’s easy to perceive setbacks negatively during this critical period. Difficulties in life could lead to cognitive distortion, in which the individual believes they’re marginalized. From what the police gathered in Chang’s phone, it appeared that he was almost completely cut off from others.
Hsu Fu-sheng
Central Police University dean
In Chang’s case, I’d say it’s due to his personal dissatisfaction with life trajectories. I believe there are more and more people of this sort. Chang was dismissed from the military, he got another job, but he only stayed on it for a year. Little by little, he became isolated from society. Someone who’s dissatisfied with their life course may turn to random killing to assert their individual existence.
In all three cases, the perpetrators acted upon feelings of extreme social rejection. Experts believe these events hinted at a higher probability for similar incidents in the future.
Tai Shen-feng
Professor of Criminology, CCU
Now that we have three such cases, our society has to face a certain reality. It’s happened repeatedly, meaning there could be many more out there with similar fantasies, but dare not act them out yet. Or perhaps they might not have entertained such acts of violence before, but now they are. Could these people be emboldened to entertain, and even act out their violent fantasies? We certainly don’t want this to be true.
How can we prevent these negative feelings from being internalized, and in turn become the catalyst for violence? With increased evidence from research, the government has worked on bolstering the social safety net.
Hsu Fu-sheng
Central Police University dean
A Japanese study was conducted on random killing. It analyzed 52 cases. The researchers concluded that they’re all related to social isolation.
Chuang Yueh-hsiang
Flying Youth mentor
Now that we’re able to identify the cause, we can perhaps reflect on those around us. Someone may start acting strangely. They may speak less. Once these symptoms appear, we should think about how to intervene through care and action so that tragedies can be avoided.
It’s not enough to strengthen connections with one’s social circle. A long-time mentor for high-risk youth, reminded us not to incite hatred.
Chuang Yueh-hsiang
Flying Youth mentor
After a young person commits a crime, they may see comments on YouTube attacking them, calling them scum or trash, or wanting them to just die. But just think here: the law protects these youths and they could be released or rejoin society to work. If they do not develop self-awareness, or if they do not reflect on themselves, and internalize all the criticisms at them, they would take that as, “Yes, I am no good. I’m violent. I want to attack you. To those that once made me suffer, I’ll make you all suffer too!” All that hatred and fear only breed more fear.
The three lives lost on that fateful day in 2025, and many more before them, are scars in our collective memory. But even more than that, they forced us to open our eyes to interpersonal, societal and structural risk factors that catalyzed violence in the very first place. The perpetrators’ individual traits notwithstanding, we can also play a part in healing our communities and prevent another similar tragedy.
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#crime #criminology #psychology #sociology #highriskyouth
2026-06-11
