 Why does Stevenson begin to suspect a connection between the crimes?
The man who had first spoken herded the tellers, Mr. Featherhall and the customers all over against the back wall, while the second man stayed next to Mr. Anderson and the door. "And that doesn't make sense, either," said Stevenson. "I believe so, yes," said Stevenson. On the way around, Stevenson said, "I believe you reported the car stolen almost immediately after it happened." By chance, a mobile television unit was at that moment on the Belt Parkway, returning from having seen off a prime minister at Idlewild Airport.
 The nature of how the crimes ended didn't add up on their own. That, as well as the signatures, make him believe there is more.
 Stevenson has an overactive imagination, similar to how a previous police officer had been.  The nature of how the crimes ended didn't add up on their own. That, as well as the signatures, make him believe there is more.  Two back-to-back crimes is too suspicious.  The alibi of Higgins doesn't add up. He admits to leaving the signature, but Stevenson doesn't trust him.