The government can legally take action without the "truth" being shown to the public and the PCs know that they were the ones to find the vital information and then passed it on to the authorities. To be a little clearer, the information isn't necessarily about evil creatures from another dimension but about something highly illegal that the enemy is doing. The fact that there are evil creatures from another dimension involved is something the government wants to keep from the public.
This can also let you give the PCs a reward in the form of a government contact who while not necessarily being able to give the PCs lots of cool gear, can order certain kinds of military/police operations to happen - so next time the PCs get involved with a really powerful enemy, they have the choice of dealing with it themselves or passing the details on to the government contact who can order a special forces group to deal with it.
Basically this means that the PCs can call in a military strike on the bad guys if they need to!
![Very Happy :D](./images/smilies/icon_biggrin.gif)
Some Players like this kind of power but others feel that it robs them of their ability to deal with the problem themselves so I'd say try it once and if the Players like the idea that's good, if not it's time to try something else
![Sad :(](./images/smilies/icon_sad.gif)