Remember your formula:
Liar/none + PE = guilty
Liar/none + WE = guilty
WE + WE = guilty
In your case you could try to continue to interview suspects and try to find the WE (witness evidence) to find the murderer.
Dead people are good because it eliminates one possible suspect, but hopefully you have gotten all the questions you needed out of them first.
The shoe print might have matched up with her but she would have had a valid (real) alibi.