Only in rare instances does an investigating officer need to explain his conduct. Glass v. State, 171 Ga. App. 156, 157 ( 319 S.E.2d 60) (1984). Chunn's own cross-examination of the officer in the present case made this one of those rare instances; his questioning of the officer made the circumstances surrounding his arrest relevant and in need of explanation.

Accordingly, its admission was error. See generally Glass v. State, 171 Ga. App. 156 ( 319 S.E.2d 60) (1984); Berry v. State, 254 Ga. 101, 105 (2) ( 326 S.E.2d 748) (1985). However, under the circumstances of this case, we find it highly probable that the erroneously admitted evidence did not contribute to the jury's verdict of guilt, and that the error was therefore harmless.