Debris of Egypt's deadly train collision removed

The video begins with a brief statement, 'I've heard that.'

What do you think the phrase 'I've heard that' implies about the speaker's knowledge?

In what contexts might someone say 'I've heard that'?

How does the phrase 'I've heard that' affect the conversation that follows?

What emotions or attitudes might be conveyed by saying 'I've heard that'?

Can you provide an example of a situation where 'I've heard that' would be an appropriate response?