Deputy national police chief Surachet “Big Joke” Hakparn delivered the news as police prepared to hand their investigation report to public prosecutors on Monday.
Surachet had previously said the report would be submitted on Friday, with the delay indicating that new evidence had come to light.
The deputy police chief said he had met with the Office of the Attorney-General (OAG)’s director of criminal cases twice and is confident that the investigation report is now complete.
Police investigators have uncovered strong evidence that a close associate of Sararat was an accomplice in four or five of the alleged murders, Surachet said.
Investigators found 200 bank and transaction records that showed the associate, who was not named, received money transfers from the murder suspect just before or after the deaths of four or five of the alleged victims, he added.
The associate will duly be charged as an accomplice in the murders.
Surachate said the charges were added to the report late as police had only recently discovered the transaction records.
“The evidence shows that the person knew about the killings in four or five cases,” he said.
Earlier, police charged Sararat’s former husband, Pol Lt Col Withoon Rangsiwuthaporn, with receiving stolen property and forging and using official documents.
Police have also charged Sararat’s lawyer, Thanicha Aeksuwannawat with helping her client destroy or conceal evidence of a crime.
Sararat has been charged with murdering 15 people with cyanide in a killing spree that spanned seven provinces – Nakhon Pathom, Samut Sakhon, Kanchanaburi, Phetchaburi, Ratchaburi, Udon Thani and Mukdahan.
Sararat was arrested on April 25 following the death of Siriporn “Koy” Khanwong, 32, a resident of Kanchanburi. Tests showed Siriporn died of cyanide poisoning.
Her death led to police investigations and complaints that Sararat may have been responsible for the deaths of 14 other people.
Most of the alleged victims owed money to Sararat. Police say all 15 alleged victims were either with Sararat or consumed food, drinks or herbs she gave them, just before they died.