I was, in fact, clearing up Mr.
Lyne's desk.

I had occasion to leave the office, and on my return found the place in darkness.

I re-connected the light, and then discovered on the desk a particularly murderous looking revolver.
"In the statement I made to you, sir," he turned to Tarling, "I said that that pistol had not been found by me; and indeed, I professed the profoundest ignorance of its existence.

I regret to confess to you that I was telling an untruth.

I did find the pistol; I put it in my pocket and I took it home.