How to know who posted them?

string user_name;
key user_key;

default
{
    state_entry()
    {
        llSetTimerEvent(0.1);
    }
    touch_start(integer a)
    {
        user_name = llDetectedName(0);
        user_key = llDetectedKey(0);
        llAllowInventoryDrop(1);
        llSetTimerEvent(20);
        llSetText("Please drop inventory "+user_name,<1.0,1.0,1.0>,1.0);
    }
    changed(integer a)
    {
        if(a & CHANGED_ALLOWED_DROP)
        {
            //was "user"
        }
        else if(a & CHANGED_INVENTORY)
        {
            //was the owner or another user with mod rights to your objects
        }
        llSetTimerEvent(1.0);//this is so they can drop multiple items without it loosing the setting.
    }
    timer()
    {
        llSetText("Please click object first before dropping inventory",<1.0,1.0,1.0>,1.0);
        llAllowInventoryDrop(0);
        llSetTimerEvent(0.0);
        user_key = user_name = "";
    }
}