A man shot dead two relatives and a policeman with a hunting rifle before killing himself on Friday, in the second shooting rampage in three days in the nation.
A 75-year-old man surnamed Jeon opened fire at a home in Hwaseong, Gyeonggi Province, at 9:30 a.m. killing his brother and sister-in-law. They were reported to be involved in a financial dispute.
The victims' daughter-in-law fled the scene, injuring her lower back after jumping from the second story of the home where the crime occurred.
A construction worker nearby who heard gunshots alerted law enforcement. But the first police officer to reach the scene was shot on arrival by Jeon. The officer was not wearing bulletproof gear.
Jeon killed himself at the crime scene after he was cornered by law enforcement officers, police said.
Police later found a letter written by Jeon in his car, claiming Friday's crime was premediated.
"I have written everything down by the book. I am sure no one has found out about my plans," the letter read, according to authorities.
"The letter indicates the crime was most likely planned out," a police spokesman said. "But we will look into what the specific motive was."
Jeon had frequently threatened his brother and his family when he got drunk, police added. Jeon was reportedly under the influence of alcohol at the time of the killings.
On Wednesday, a similar shooting in Sejong left four people dead. The killer had shot three people near a local convenience store, and killed himself a few hours later. The killer, surnamed Kang, set the store on fire after shooting his victims.
The victims were the boyfriend and family members of Kang's ex-girlfriend. Police think Kang committed the crime out of revenge, and disagreements over money with his former partner.
Police said they would seek measures to make it more difficult for people to own guns.
Both Jeon and Kang used hunting rifles, weapons usually stored at local police stations. Authorized gun owners can take out their guns in only at certain times of the year and certain times of day.
Hunting rifles are allowed to be taken out by owners in the hunting season, which begins in November and ends in February.
More than 160,000 guns are stored in police stations. They include an array of rifles ranging from air guns to pistols.