Charnchai surrendered to police on Monday and was charged with trying to bribe Krairerk to vote against dissolution of a political party.
Chief investigator Pol Lt Gen Chongrak Chutanont said after questioning Charnchai for two hours that the suspect denied the charge, saying that he was just joking when he offered Bt30 million to the judge.
"Pol Col Charnchai said he visited ML Krairerk at the Supreme Court office just to invite him to a reunion party of Thammasat University's law graduates. His visit was also to congratulate Krairerk, supreme court vice president, in being appointed a Constitution Tribunal judge," Chongrak said.
"He admitted that he said something about the bribe, but he claimed that he just made a joke," Chongrak added.
Charnchai was quoted as denying that he was hired by a political party to bribe the judge.
However Chongrak said Krairerk's claims that Charnchai offered him a Bt30 million bribe and that he rejected it seemed to outweigh Charnchai's testimony.
Charnchai's lawyer said that he will seek Bt200,000 bail for his client.
Charnchai was named as the person who offered Krairerk the bribe in an attempt to prevent Thai Rak Thai Party from being dissolved.
The Criminal Court on Wednesday last week approved the arrest warrant after Krairerk confirmed in his documents to the court that Charnchai had tried to bribe him to vote against the TRT dissolution, but Krairerk rejected the offer.
Chongrak earlier said that although the judge did not accept the bribe, the offence was committed and the suspect should be prosecuted.
Justice Ministry permanent secretary Charan Phakdithanakul dropped the bombshell bribery allegation in June, saying a senior official tried to secure a "not guilty verdict" for TRT by offering money to the judges.
Later, Weera Somkwamkid, secretary-general to the Anti-Corruption People's Network, asked the police to investigate a report that high-ranking court officials and a police colonel who graduated from Thammasat University's Faculty of Law in 1966 had offered bribes to Supreme Court judges who also acted as Constitution Tribunal judges.
An ad-hoc panel of the Supreme Court found that court officials who are not judges were involved in the bribery. They understood that Krairerk and Supreme Court judge Somchai Pongsatha were offered bribes and that both refused to accept them.