Police investigating what happened to £10.25m of public money loaned to Northampton Town for a new east stand which was never completed have said that potential offences being considered include theft, fraud, money laundering, bribery and misconduct in public office.

A spokesman for Northamptonshire police explicitly described the case, Operation Tuckhill, as in the category of “complex financial and corruption investigations”.

The £10.25m was loaned by Northampton borough council in 2013-14 to pay for the stand and other improvements to the club’s Sixfields stadium, and the club contracted a company called 1st Land, whose director was Howard Grossman, to oversee the project. The developer, Buckingham Group, downed tools with only the shell of the stand built, said publicly that it had been paid £442,000, with £1.9m still owing, and in January 2015 put 1st Land into administration.

The council ultimately complained to police that a very substantial proportion of its loan was not accounted for and the police executed a warrant to search the stadium in November 2015. In February this year Grossman was disqualified from being the director of any company for 10 years, following an investigation by the administrators. The Insolvency Service said in its statement that Grossman had caused £5.6m to be paid out to “various parties”, including £1.5m to himself, after 1st Land received £6m from the council.

Giving an update on the investigation, the spokesman for Northamptonshire police said: “A dedicated police team continues to investigate the disappearance of £10.25m lent to Northampton Town football club by Northampton borough council in 2013-14.

“In addition to speaking to witnesses and suspects, this requires the detailed analysis of vast amounts of data obtained from multiple sources. Complex financial and corruption investigations often take significant time before charges can be made and, in this case, there are a higher than usual number of individuals under investigation for theft, fraud, money laundering, bribery and misconduct in public office.

“We are in regular contact with the crown prosecution service to update them on our progress. While the public may understandably find the length of the investigation frustrating, it is necessary to build a robust case that results in both fair trials and safe convictions.”