Documents including receipts and authorisations of payments related to the 2023 Pacific Games are reported to be missing and suspected to have been destroyed.
The Solomon Islands Independent Commission Against Corruption and the Solomon Islands police are investigating.
"These documents are crucial to the investigation and their disappearance could distort a full and balanced audited report," an anonymous source told the Solomon Star.
"It is possible these documents have been destroyed."
The revelation came as the multinational KPMG team of accountants based in Fiji arrived in the Solomon Islands on Thursday to look through the books.
This comes on the back of police confirming a separate investigation into an allegation of abuse related to the $US309 million Economic Stimulus Package in the country, based on referrals from the Solomon Islands' auditor-general's office.
Auditor-general David Dennis recently told a news conference that financial statement audits from the National Hosting Authority for 2019 through to the end of 2021, in addition to an unnamed special procurement audit, are anticipated to be reported by the end of March.
Mr Dennis said "ongoing challenges" in obtaining requested documentation from the National Hosting Authority over the Games continue to delay the completion of the financial audit.
"To date, proper documentation to support the validity of actions and transactions for certain major procurements has not been provided and remains a concern," he said.
"Updates on the expected completion dates for the remaining financial audits covering 2022-2024 will be shared later."
Prime Minister Jeremiah Manele has relieved his own PM's secretary, Dr Sir Jimmie Rodgers, of his duties to allow him to prioritise investigating the audit process to present to parliament while assisting in securing finances to organise a series of 2025 international and regional events.
No official in the Solomon Island Games National Hosting Authority nor in the government can confirm the total cost of the quadrennial event hosted in Honiara 15 months ago.
According to estimates generated from an online search, the 2023 Pacific Games cost somewhere between $US250 million and $US355.5 million.
Foreign aid – particularly from China – contributed to a large portion of the cost, focused on infrastructure development like Solomon Islands' new National Stadium.
The increasingly close relationship between the governments of China and the Solomon Islands has come under scrutiny, including criticism from within the Solomon Islands.
The Pacific Games has spurred major investment in infrastructure upgrades beyond just sports facilities, contributing to the increase of overall costs.
While a significant expenditure for the Solomon Islands, the government has maintained the hosting of the Games that included Australian and New Zealand athletes was an economic boost due to increased tourism and investment.
Part of the concern is whether Solomon Islands officials personally pocketed funds from the foreign investment.
Dr Charles Hawksley has more than 30 years of experience in both fieldwork and research in politics and development of the Pacific Islands and is an expert on how Pacific Island states work with aid donors.
The senior lecturer at the University of Wollongong was one of the first commentators to point out that the cost of the Pacific Games would be an economic and political issue.
"Estimates of overall costs vary, with a November 2023 estimate placing the total cost at $US250 million and another from June 2023 at around $US355.5 million," he wrote in the EastAsiaForum, an analysis publishing forum.
"If the latter estimate is accurate, the cost of the Games may be equivalent to around 46 per cent of the country's annual budget and 22 per cent of its 2022 GDP.
"There is no doubt that the Games are a major expense, surpassing even the initial $US210 million cost of the Tina River hydropower project."
