The motive behind the murder of the Japanese woman...

"Because I was afraid to die alone"... A man in his 30s killed a Japanese woman in Cheonan (Comprehensive)
n.news.naver.com
Reporters Lee Si-woo and Choi Hyung-wook = A man in his 30s who killed a Japanese national and fled from an officetel in Cheonan, South Chungcheong Province, has been apprehended by the police. The Cheonan Seobuk Police Station announced on the 29th that they have arrested and are investigating Mr. A on suspicion of murder. Mr. A [committed the crime] at 4:20 PM the previous day.
Is he insane? If he wants to die, he should just die alone..