In a case like this, it can be hard if you are new to helpdesk or feel like you want to trust your coworkers to be professional and to feed you all relevant information that they could have. But they rarely do, even other IT people. The nature of end users (the coworker becomes an end user in this scenario) is to hold back the info, or to attempt to "interpret" it through their vision of what's happening.
But here is the problem: the person stating the problem (that they cannot solve) is the one person we are sure can't tell us everything that we need to know because, if they could, they'd be able to solve the problem (in most cases.) So the person who most wants to "filter" what is said, is the person least likely to be able to determine what a good filter is. Even a well meaning person in that position isn't useful.