Network performance monitoring

I'm looking for a solution to a network performance issue. I have a site where users are complaining about response time. I've relocated one of the users to a different site (physical building) along with their computer, phone and all peripherals to find out if response time improves which it has. I'm having this person remain at the alternative site for a week to continue with the test, which I initially thought would either prove of dis-prove that the network was the issue and not the application or the database. So far, as stated above, performance has noticeable improved according to the user but I'm guessing that I will need more proof than just the users observation and experience to bring to the network team. This is why I'm looking for suggestions that I might use to support my case.

Thanks,