House Taken Over

Why does the writer give so little details about the intruders?

"......I heard something in the library or the dining room. The sound came through muted and indistinct, a chair being knocked over onto the carpet or the muffled buzzing of a conversation...... I hurled myself against the door before it was too late and shut it, leaned on it with the weight of my body; luckily, the key was on our side; moreover, I ran the great bolt into place, just to be safe