How to sound like Jem in to kill a mockingbird?

[Lissa]

I want to write a diary entry outlining the thoughts and feelings upon realising that Tom Robinson was killed whilst escaping jail in Jems point of view. I want to know how I can learn how to be in his shoes and talk like him for my diary entry.

So how would I write a diary entry that makes you immediately think of Jem. How do I form his voice in my peice?

Thank you all in advance!