Split the party when ever possible.
Provide multiple places where research needs to be done then limit the time that it can be done in. That tends to force the group to split up.
Don't always take a player out of a room when something terrible is about to happen to them that other players would not know about. Torture the other players by letting them know the horror that awaits them while they are unable to do anything to save their friend.
Cut between the different groups never spending more than a few minutes describing events at each scene, build lots of "mini-cliffhangers" into the switching. Say one group is researching 'alone' in a library have then hear a book fall off a shelf a few rows down, but then switch to the other group. This allows the tension and suspence to build.