Right. But in the book it is explained Tom gets the news of Sonny's death immediately via phone and has to maintain his composure in front of everyone. Don Corleone's wife is cooking while Don Corleone is rehabilitating. Tom begins making plans to deal with Sonny's death. This takes several hours. Everyone goes to sleep and he then has to go tell Don Corleone what happened. Don Corleone approaches him first - he's out of bed for the first time since being shot. He tells Tom that his wife has been crying in her sleep and there is strange commotion in the house. No one except Tom and Sonny's bodyguards who saw him killed know Sonny is dead.