Foyle inclined his head. His blue eyes were alight with interest which he made no effort to conceal. He half guessed what was coming, but he found Grell's ways disconcerting and could form no certain judgment. Certainly Grell did not behave like a guilty man—that is, a man guilty of murder. But neither did he behave like an innocent man. He was too totally unconcerned with the gravity of his position.
"Yes, there were finger-prints," he said. "I have a photograph of them in my pocket if you would like them compared now."
"With mine? That's what I was about to suggest. You'll find some writing-paper and ink in the desk behind you. I suppose they will do."
The prisoner smiled as he saw Foyle carefully shift his chair to guard against any sudden rush, before turning his back. He was a moment preparing the materials and then placed a blank sheet of paper on a little table in front of Grell. "Will you kindly hold out your hands?" he said. As Grell did so he smeared the tips of the fingers of the right hand with ink. "Now press your fingers lightly but firmly on the paper. Thank you."
He brought a little standard lamp closer, and under its rays studied the two sets of prints closely. He did not need a magnifying-glass to see that none of Grell's finger-marks agreed with the two that were clear on the dagger. Grell leaned back in his chair as though the matter were one of complete indifference to him.
"Does that satisfy you, Mr. Foyle?" he asked at last.
The superintendent nodded as their eyes met. "It satisfies me that you did not actually kill the man," he said steadily. "I'll own I'm not surprised at that. I believe if you had killed him you would have been man enough to have stayed and faced the consequences. You will observe that I have not formally arrested you yet. But I do believe that you know all about the crime—that you were perhaps an eye-witness."
For the first time during the interview Robert Grell lost hold of his self-control. His fists clenched and the steel of the handcuffs bit deep into his wrists as he momentarily forgot that he was handcuffed. There was a meaning in Foyle's tone that he could not fail to understand. He caught at his breath once or twice and his temples flamed scarlet.
"Speak plainly now!" he cried hoarsely. "What are you hinting at?"