The candy robber

Jack was getting a lot of money.

It would look bad if a detective agency got robbed, he thought. I’d better take this money to the bank. He walked downtown and put his money in his bank account.

As he walked back to his agency, he found a small boy. The boy asked him “Do you know where Jack’s Detective Agency is?”

Jack replied: “I’m Jack, what do you want me to help you with?”

Jack led the boy to his agency, the boy told his story.

“I’m Theodore Smith, but everyone calls me Ted. I had bought some sweets from that corner shop when an older boy saw me. He offered to buy those sweets but when I said no, he snatched them off me.”
Jack asked “Who do you think snatched him off you?”

Theodore replied “He said his name was Ernie.” 5 seconds later Jack was in Ernie’s gang’s den. Ernie welcomed them warmly.

“Get out”.

Jack sat himself on a chair and introduced Theodore to Ernie. “This is my client ,Ted Smith, and he says you stole his sweets.”

Ernie said: “Well I did have some sweets just now, but my uncle gave them to me.”

At that moment Charlie and Roger rushed in. They were part of Ernie’s gang. “Who’s this?” they said, pointing at Theodore. “Theodore Smith,” replied Ernie. Jack asked Theodore: “How much did those sweets cost?”

“About £3.50. I might’ve been wrong. Must’ve thought he said Ernie or something. Let’s leave.”

“Not until Ernie pays the £3.50” said Jack.

How did Jack know?