The former Thai MP accused of shooting dead a local official had gone to him asking for money, according to police and his own account of the killing, which came just days after a mass school shooting.

Chalong Reawraeng, 71, former MP for Nonthaburi, said he had gone to his long-time friend Thongchai Yenprasert, also 71, to ask for the money he had lent him years earlier, and ended up shooting him dead.

Mr Chalong served three terms as MP. He came to be known as “cobra”, a term used in Thailand for a politician who breaks ranks, after defying his party in 1997 to vote for a prime ministerial candidate from another party.

He was most recently a lawmaker for Pheu Thai, the party built around the Shinawatra family which dominated Thai elections for a generation. At the last election, however, he switched to Bhumjaithai, the party of the prime minister, Anutin Charnvirakul, but failed to win.

Mr Chalong said he needed the money because he had been receiving treatment for polycythaemia, a condition of the body producing too many red blood cells, since 2011 and he could no longer bear the cost. He said he had lent the money to Thongchai years ago when he was struggling in his property business.

Thongchai, a former police colonel who had run the local authority in Nonthaburi, a province on Bangkok's northern edge, since 2004, refused to hear him out.

“Today I went to talk to my friend in his office. We spoke and he didn't listen to me," Mr Chalong told a press conference at the police station where he was detained. "He pushed me, saying, 'I don't want to talk. I don't want to talk'. Then he started walking.”

"I followed him to his car and hit his car's window, saying I wanted to talk. He said he would not talk, so I pulled my gun," he said. "I did not aim to shoot, but his driver pulled a gun and pointed it at me so I fired."

Thongchai was shot four times, including in the neck, and lost a great deal of blood. He died later at the Phra Nang Klao Hospital in Nonthaburi, its director Sakol Sookprome told Reuters. His driver was shot in the right arm, had surgery and was reportedly out of danger.

Mr Chalong apologised to his former constituents and said that he never intended to shoot a man he considered a good friend.

"I can't believe I'm in this position, sitting here,” he said. “Throughout my life, I never had to come to a police station.”

Police said Thongchai had borrowed several million baht from Mr Chalong and had been asked to repay the money several times.

"The motive was personal," police lieutenant general Wattana Yijin told reporters. "According to his confession, it was about money that the chairman had borrowed from him for several years, and he asked for the return of the money several times."

Though both men were armed, only Mr Chalong fired, police said, adding that they found a gun unused in Thongchai's vehicle. CCTV footage showed Mr Chalong firing from close range.

Instead of leaving the area, Mr Chalong called a YouTube programmer, Anchalee Paireerak, a former journalist, and shared what he had done. Although he could not be heard, her reaction to the call was broadcast: "Did he die? Did he die? You shot him in the head? You need to wait there for the cops. Don't go anywhere.”

Thongchai joined police in 1984 and rose up the ranks to become deputy superintendent and then superintendent before being appointed chairman of the provincial administrative organisation, the elected body running local services and public works, in 2004.

His death came three days after a 14-year-old boy in Nonthaburi shot dead relatives at home and then opened fire at the Debsirin Nonthaburi School, killing eight more people and wounding over 20 in what was Thailand's deadliest mass shooting in nearly four years.