Cho Sun, who stabbed a man to death and injured three more in Seoul, had searched online for information about another stubbing rampage in Hong Kong early last month, police said Thursday.

Gwanak Police Station is investigating the connection between Cho's Internet search record and his crime by analyzing his mobile phone and computer data from January.

The Hong Kong stabbing that Cho had searched for seems to refer to a case in which a man in his 30s wielded a weapon to kill two women in their 20s at a shopping mall in Hong Kong on June 2. The perpetrator of the case was not acquainted with the victims, just like Cho had no personal connection with the four victims he had murdered or injured.

However, the police said they would continue the investigation as it is not clear at the moment whether Cho has been considering the crime since last month.

The police also confirmed that Cho had searched for information about mental hospitals such as forced hospitalization, the cost of treatment and fleeing from them. The Hong Kong killer was found to be suffering from mental illness.

Cho had reportedly stated in a police investigation that he had suffered from symptoms of depression, but according to the police investigation, they had found no medical records of mental illness from January 2013 to the day of the crime.

Earlier on Wednesday, police obtained a statement from Cho that "I had searched for the method of murder, the vital point, and the type of knife that kills people."

Cho stabbed a man in his 20s to death near Sillim Station on Seoul Metro's Line No. 2 in Gwanak-gu, southern Seoul, at 2:07 p.m. Friday. He also injured three other men in their 30s. He was caught at the scene of the crime and was arrested Sunday on suspicion of murder and attempted murder.

The Police held a Personal Information Disclosure Committee on Wednesday and decided to disclose Cho’s name, age, and picture, in recognition of the cruelty of the crime and the seriousness of the damage. A psychopathic diagnostic test was also conducted on him, but the results are yet to be released. Cho will be sent to the Seoul Central District Prosecutors' Office Friday.