One person has been charged and two are still being questioned by gardai investigating 11 suspected arson attacks in South Inishowen since July.
A 17 year old youth was charged at Buncrana Garda Station last night. He was released on bail, to appear at Buncrana District Court on the 8th of September.
A second man remains in custody in Buncrana, and is still being questioned.
Of the two men being detained at Letterkenny Garda Station, one man has been released pending a file to the Director of Public Prosecutions.
The second remains in custody.
The four were among five men aged between 17 and 24 arrested since Wednesday - One was released without charge on Wednesday night.