What are some of juror 8's reasons for his uncertainity about the defendants quilt?

In Act I, the 8th juror defends his “not guilty” vote for the boy. He states that he’s not sure whether or not the boy did it, but he was unsatisfied with the job of the defense council, and he was unsure of the two eyewitnesses. This leads into a discussion about the knife. 4th Juror explains that, on the night of the murder, the boy bought a uniquely carved switchblade knife identical to the one used in the murder. The boy claims that he lost it that night, before coming home to find his father dead. 4th Juror presents the death weapon, the “only one of its kind;” 8th Juror surprises the others by presenting an identical knife he had purchased in a pawn shop two blocks from where the boy lived a few nights prior, shattering the claim that the knife was unique and identifiable. An argument breaks out among the jurors as to the new doubt; most are just upset that they’re still arguing and want to just declare him guilty and go home.