IMO, not really a nightmare to prosecute.
If they have solid irrefutable evidence like the perpetrator(s) DNA at or near the crime scene, phone records, etc.
The prosecution will weigh the evidence they have and not introduce anything that is "iffy" as far as possible cross contamination, etc. It is very normal for investigations to go back to certain things once they start getting actionable leads. the fact that they didn't search every yard early one doesn't really matter.
Seeing hundreds of cases, again.. IF they have vert solid forensic evidence, this will probably prosecute pretty well.
JMO