My main technique for events that the main character did not witness: Show the delivery.
And given that the main purpose of showing is to allow the reader to share the character's experience: Make the delivery, and not merely the information itself, an important experience.
Here are some things you can show:
- The information being delivered
- Who is delivering it
- The manner in which it's being delivered
- What the main character thinks and feels about the information, the person delivering it, and the way it's being delivered
And you can play with those things in ways that affect the main character's experience, and so the readers' experience.
Here are some other fun variables you can play with:
- How direct is the information? Did the side characters participate in the events they're describing? Witness them? Hear about them from someone else? This offers possibilities for their stories to inadvertently omit, add, or distort the details of what happened.
- What did the side characters observe? Each will observe from a different vantage point. So each will attend to different things, and each will care about different things as events unfold, and each will interpret the events differently. This offers possibilities for their stories to inadvertently omit, add, or distort the details of what happened.
- What are the side characters' agendas? This will lead them to observe and interpret events differently. And it may lead them to deliberately withhold, add, or distort details as they related them to the main character.
- The side characters' knowledge, beliefs, and values may differ from the main character's. So they may react in ways that support or interfere with what the main character wants.
- Readers have access to the main character's thoughts, but not the side characters'. So they know what the main character cares about, but not what the side characters care about. This allows you to play with readers by leaving the side characters' knowledge and agendas ambiguous.
- Side characters may differ among each other in what they witnessed, and in their agendas. Different side characters may tell different stories.
These things offer lots of possibilities for misunderstanding, confusion, misdirection, betrayal, manipulation, conflict...
You can use the delivery to show some of these things. Others you can't, because the main character can't observe them directly. But you can use those hidden things to set up other events that you will show later.
The main idea behind all of this: Make the delivery itself a significant experience for the main character, and show it so that the reader shares the experience.