Goodtime Slim's Solve-Your-Own Mystery

Can you guess the identity of the killer from the story below?

Lady Earnshaw surveyed the people gathered in the drawing roon of the large, elegant country house known as The Cloisters. There was Mr Carstairs, the famed explorer; Lord Ridlington-Smythe and his son, Augustus; Miss Riley and her betrothed, Mr Farndale, and Evanns the butler.
"Thank you for your time," Lady Earnshaw addressed them all, "I pray that this will not take long. For I have gathered you all here to tell you that I have found the identity of the person who killed the parlour-maid!"
"I did," replied Augustus.
"As you know, the foul deed took place in the conservatory at midnight," continued Lady Earnshaw.
"I killed the bitch," interrupted Augustus, cleaning his fingernails with a bloody knife.
"The parlour-maid was stabbed 142 times in the buttocks and lower back."
"Yes, by me," stated Augustus baldly.
"That's right," said Lord Ridlington-Smythe, "I saw the whole thing."
"And me," interjected Mr Carstairs.
"And now the time has come for me to expose the killer!" Lady Earnshaw thundered dramatically. She raised an accusing finger at Evanns, the butler. "It was you!"
"No!" everyone gasped.

Q. How did Lady Earnshaw know that Evanns was the killer?

A. She didn't. Lady Earnshaw had been certifiably insane since her husband died on the Somme, and what's more she'd been hitting the gin all day. The real killer was Mr Farndale, who had been born a commoner, whose eyes ere too close together, and who had used the wrong fork for fish at dinner.