If an ex-con who committed that very crime comes up as suspect and evidence points to their guilt, how much would they investigate other angles? In my case, he was framed and re-jailed, but a year later one brilliant detective finds the inconsistency the others all missed. But originally, how much would they investigate? I see in some shows that brilliant detective finds out that the original investigation was also shoddy or excluded evidence like that one unidentified fingerprint, etc.
Oftentimes, Occam’s razor is at the basis of policing, that is, simpler solutions are more likely to be correct than complex ones. If evidence points to the ex-con and the ex-con had committed that crime in the past, then the police would not immediately think that it is a frame job. Some evidence lead to dead ends, i.e. unidentified fingerprint, but between a dead end and a likely end the police would choose the more likely result of where the evidence leads them. Most crimes are straightforward and do not need a complex investigation because most criminals do not commit complex crimes. Some pieces of evidence only become clear in hindsight, this does not mean that the original investigations were shoddy only that time was needed to see where the evidence truly lead.
