Why does redeclaring a function identifier within a try block throw a SyntaxError?

The following lines of JavaScript

try {
    function _free() {}
    var _free = 1;
} finally { }

result in the following error:

 Uncaught SyntaxError: Identifier '_free' has already been declared

However, the following two blocks of JavaScript code don't:

1. Without the try block scope:

   function _free() {}
   var _free = 1;
   

2. Within a function scope:

   function a() {
       function _free() {}
       var _free = 1;
   }
   

But why?

(Testing environment: Chromium 61.0.3126.0)