I have a few criminals in my books. For example, in All the Better to Love You With, Mandy Hood (Red Riding Hood) is arrested for stealing her grandma's car so she could visit her other grandma. She's pulled over by Sheriff Brad Wolfe and put in jail.
I had to do a bit of research on what happens in jail for this book, and a few others where I had the main character go in jail (I have a few of them). But the character changes once they're in jail. They feel like a failure, that all hope is lost. Their lives change and they become more humble.
The character is in jail for a reason. Sometimes, it's to get information for their job (undercover). Sometimes, it's because they did something wrong. And sometimes, they're standing up for what they believe is right.
Whatever your criminal does, make them feel like they've lost all hope. They're stuck in jail for a reason, and they're now at the mercy of law enforcement and the other inmates. The code inside the jail is different than outside, too. From what I understand, there are social classes and other issues that normal people don't encounter.
Am I missing anything?
Have a great day!