A wave of online posts threatening murder and attacks is heightening the sense of concern and unease over possible copycat crimes targeting strangers in the aftermath of two stabbing rampages in Seoul and Seongnam, Gyeonggi Province.

The National Police Agency said in a press conference Monday that it has tracked down 59 people for posting murder threats on the internet and arrested three suspects, after identifying 187 threatening posts.

Police said that out of 59 people, 34 are teens, including minors who are too young to face criminal charges. The act of posting online threats is rapidly spreading following high-profile unprovoked attacks against strangers in recent weeks.

On Thursday, a man rammed a car onto the sidewalk and attacked shoppers with a knife at a department store in Seongnam, Gyeonggi Province, leaving one person dead and 13 people injured. The store is connected to the busy Seohyeon Station, frequented by commuters and shoppers alike.

On Saturday, the Suwon District Court granted a warrant to formally arrest the 22-year-old suspect on charges of attempted murder.

On July 21, a man similarly went on a stabbing rampage near Sillim Station in Seoul, killing one man and wounding three others. All the victims were strangers to the suspect, surnamed Cho.

It is deeply shocking to witness such violent crimes committed in a country known for a relatively high level of public safety. It is all the more worrying that the perpetrators target innocent strangers at random in crowded places, catching the police off guard and sparking alarm among residents.

A thorough investigation to identify the specific motives of the horrifying crimes should be carried out. At the same time, police must take steps to prevent copycat crimes, including online threats, from spreading further.

Police asked the Education Ministry and related authorities to cooperate in efforts to prevent crimes among teenagers and young adults in connection with online murder threats. Since the rampage in Seongnam, police have checked 442 passersby who were seen to exhibit strange behavior, and booked 14 suspects on charges of threats, possession of weapons and other crimes.

Separately, a 31-year-old individual was arrested for allegedly threatening to commit violent crimes at Hyehwa Station in Seoul. Police also investigated a 17-year-old for uploading a post on social media threatening to embark on a stabbing rampage at Wonju Station in Gangwon Province.

Similar online murder threats -- mostly targeting strangers in public places -- are being posted across the nation, prompting police and authorities to track down on suspects.

Some experts raised the possibility that the latest rampage itself is a copycat crime, tracing back to the similar crime that took place near Sillim Station in Seoul last month. The suspect reportedly searched “Sillim Station” and “knife” before committing the crime himself.

To prevent copycat crimes, police and law enforcement authorities should join forces to track down all suspects who post murder threats on social media and take strong measures against criminals without delay.

At the same time, policymakers have to consider the critical issue of the police response to violent crimes. Some police officers face lawsuits for hurting suspects in the process of preventing a crime. Fearful of lawsuits, some police officers may act passively when confronting suspects at the scene of a crime.

Last year, the related law was revised in a way that lessens the legal burden on the part of police officers regarding the excessive use of force, but the law does not apply to civil lawsuits.

Justice Minister Han Dong-hoon said Monday the use of force by police when arresting violent criminals should be considered self-defense and called on the prosecution to apply the self-defense rule to such cases.

Strengthening punishment against violent crimes is also needed. Lawmakers have filed a host of revision proposals at the National Assembly, aiming to step up punishment against crimes targeting strangers. Both ruling and opposition parties must hurry up on starting legislative discussions over the revision.

The government should also come up with proper measures to prevent unprovoked crimes against strangers, while taking steps to enhance overall public safety.