US Senator Van Hallen (from Maryland) flew down to El Salvador managed to see him after applying a bunch of pressure in mid April. So he was at least alive then. Photos were published and such of said meeting
Other dems from congress have flow down besides Van Hallen, but haven't been able to get a visit. They've also had a ton less media attention, so there was less pressure on El Salvador to let them visit him. For instance, Glenn Ivey traveled to El Salvador and tried to visit a week ago but I doubt most people here probably heard about that
They're continually paying El Salvador for this on an ongoing basis per Chris Van Hollen. To a place they could easily withhold funding if they wanted to until he was sent back