In the 21st century, innocent people routinely accept plea deals to avoid the risk of trial. The corroborating evidence need not be strong because the threat of the trial penalty is enough when you can't afford a good lawyer.

https://innocenceproject.org/coerced-pleas/

>The prosecutors have to have corroborating evidence.

Bla bla bla, prosecutors are the good guys and show all the evidence they have....

Um, not.

We keep finding again and again we're putting innocent people in jail even for things as serious as capital crimes, and later it was found the investigation was botched and there was no evidence that person was guilty and other evidence was never presented.

wrong. confession is the pimary way most people get convicted