Prosecutors are seeking the death sentence for Prasittichai Khaokaew, the school director-turned-killer who robbed a gold shop in Lop Buri last month.
The Criminal Court was asked on Thursday to try the 38-year-old over the armed robbery at Aurora Gold Shop in Robinson shopping centre on Jan 9, in which he shot dead three people -- including a two-year-old boy -- and wounded four others.
Mr Prasittichai initially claimed he robbed the shop for "some excitement" in life. However, a source close to the investigation revealed he desperately needed money to settle debts of over 2 million baht.
According to investigators, Mr Prasittichai used a CZ P-01 gun borrowed from his father's house and fitted with a silencer which he later threw into a river.
He made off with gold weighing 28.5 baht, worth about 635,000 baht.
"We have to convince the court his confession doesn't mean he has repented, it simply means he gave in to the weight of evidence," deputy Criminal Litigation Department chief Phonchai Chonwanitkun said on Thursday.
"More importantly, his cooperation does not benefit the trial. But whether the suspect receives harsh penalties will depend upon the court," Mr Phonchai said.
Prosecutors studied a police report sent on Feb 11 and decided to charge Mr Prasittichai with nine crimes, including killing a person to commit other offences, robbery, illegal possession of firearms, and firing a weapon without sound reason.
In a separate development, the mother of Danusorn Numcharoen, 28, who shot dead his ex-wife at a cosmetic surgery clinic in a Bangkok shopping mall on Tuesday, said her son had planned to harm Piyanut Chatthai, 28, following their divorce.
"He couldn't forget his ex-wife even though they had split," the mother said on Thursday as she visited Mr Danusorn in detention at Phayathai police station.