ロバート・ハンセンが、旧ソ連に秘密情報を売りさばいた容疑で逮捕された。

・、。

Robert Hanssen was arrested on suspicion of selling classified information to the former Soviet Union.

Literal

Robert Hanssen [subject-が], former-Soviet-Union [to-に] secret-information [object-を] sold-off suspicion [with-で] was-arrested.

A news report sentence. 旧ソ連 (former Soviet Union) uses the prefix 旧 (former). 売りさばく (sell off/peddle) is stronger than 売る — it implies selling recklessly or illicitly. 容疑で (on suspicion of) is standard legal/news phrasing. The passive 逮捕された is natural for reporting arrests.