How to determine why port 443 is already in use?

The issue appears to have been Apache conflicting with itself due to there being two Listen 443 directives, the one I added and one via include:

<IfModule ssl_module>
#Include conf/extra/httpd-ssl.conf
Include conf/extra/httpd-sni.conf
SSLRandomSeed startup builtin
SSLRandomSeed connect builtin
</IfModule>

In the conf/extra/httpd-ssl.conf appears the conflicting line:

Listen 443 https

Dropping the Listen 443 I added resolved the issue.

c:\Apache24\bin> netstat -ano | grep 443

will list all processId bind 443, like:

 TCP    xxx:xxx     xxx:443      ESTABLISHED     4332
 TCP    xxx:xxx     xxx:443      ESTABLISHED     7164

then execute:

c:\Apache24\bin> tasklist | grep -e "4332" -e "7164"

will list all process by Id. like:

MyPopo.exe                    4332 Console                    1     87,424 K
firefox.exe                   7164 Console                    1    522,576 K