Final answer:
The police retrieved the evidence through identification procedures and eyewitness testimonies. Suggestive police identification procedures can lead to incorrect identifications, while cautious handling of eyewitnesses helps avoid false memories or misleading information.
Step-by-step explanation:
The police retrieved the vital piece of evidence leading to the killer's identity through identification procedures and eyewitness testimonies. In some cases, suggestive police identification procedures can lead witnesses to incorrectly identify a suspect, as seen in the Ronald Cotton case. These procedures include stacking lineups, telling the witness which person to identify, and confirming their choices. On the other hand, cautious handling of eyewitnesses, as demonstrated in the Elizabeth Smart case, aims to avoid implanting false memories or misleading the witnesses in any way.