Operation Teal started in January after "matters of concern" were raised by Tayside Police about the way drugs squad officers obtained information.
The Crown Office has now instructed neighbouring Grampian Police to investigate allegations against 24 officers.
The interviews, understood to involve current on-duty detectives of different ranks, will continue in the next few weeks.
A Crown Office letter was sent to the officers advising them to get legal representation.
It stated: "Grampian Police has been instructed by the Crown Office and the Procurator Fiscal Service to conduct an external force investigation into several inquiries which were dealt with by Tayside Police.
"As a result of the investigation to date, you will require to be interviewed as a suspect in respect of a criminal allegation."
In May a drugs squad officer, 40, was suspended and charged with assault. A 27-year-old officer was also charged with assault as a result of Operation Teal but Tayside bosses said he was not a member of the drugs squad.
Around the same time, two senior detectives were also understood to have been transferred out of the drugs squad.
In May last year, Stuart Sandeman, who had convictions for drug dealing, collapsed and died in a raid at his Perth home carried out by the force. Sandeman was reported to have wrestled with officers during the raid.
There is no suggestion the conduct of officers contributed to his death, which was reported at the time as "unexplained".
A Tayside Police spokesman said it "identified matters of concern about the working practices of certain individuals with the procurator-fiscal".
He added: "It was requested that Grampian Police conduct an independent investigation into the full circumstances. A number of police officers have spoken with the investigation and officers will continue to assist the inquiry team as required."
North East Labour MSP Jenny Marra said: "Eleven months seems too long for this type of investigation."
Tory MSP Alex Johnstone, who also covers the north-east, said: "Anybody over-stepping the mark should be charged and held accountable for their actions.
"I have sympathy with the situation the police find themselves in. There has to be further investigation and I am confident Grampian will carry that out."