Why did the mechanical hound and camera incriminate an innocent man?

Montag needed to be dead, and his death needed to be public and definite. Since Montag escaped, a substitute was needed to convince the people he was gone.... thus, the bewildered bystander was substituted for Montag. They incriminates an innocent man because they couldn't locate Montag. The people couldn't learn he'd escaped because knowing that would encourage more people to try.

"The camera fell upon the victim, even as did the Hound. Both reached him simultaneously. The victim was seized by Hound and camera in a great spidering, clenching grip. He screamed. He screamed. He screamed!"

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"They didn't show the man's face in focus. Did you notice? Even your best friends couldn't tell if it was you. They scrambled it just enough to let the imagination take over. Hell," he whispered. "Hell."