Which account does Decisions use to install?

1. While installing the Decisions, in one step it asks for user account. For example, I used Account-1.
2. In the next step for Database Setup, I chose the Windows authentication. Our Sys Admin (for example Account-2) is installing Decisions on the server.
   In this case, since I mention Windows Authentication, does the installer use Account-1 or Account-2 for the Database operations?

Why this question is, if Decisions use Account-2 for all database operations, I should give Account-2 access to the Database.
And in different times, different user from Sys Admin team performs the installation.