Hilchos Lashon Hara chapter 7, section 4

The same applies if rumour spreads that someone did or spoke in contravention of a severe or less severe Torah prohibition. One may not believe the rumour but only suspect it is true until the matter is clarified. Even more, one should be careful if one says the story to others not to have intent to spread the story further as explained earlier (2:3), look carefully there.