From what Miriam said, it was enough to make Dominic the prime suspect. On the day of Heaven's death, there were only a few people in the mansion. In other words, a killer in the house could execute his or her wicked plans smoothly.
It could be considered premeditated; a plan Dominic had come up with months ago, creating an opportunity for someone he hired to do the job without a problem. Considering the original Heaven's mind was a maze of suicidal thoughts, it wouldn't be surprising if her killer made it look like a suicide.
If Hera didn't wake up in this body, Miriam would've arrived that morning with Heaven's cold body. However, she was so certain Dominic was innocent. Even so, the authorities would think otherwise if they got hold of Heaven's cold body that day.
After all, in this type of crime, it was always the husband.
But she was a hundred percent certain Dominic was innocent. If anything, it appeared someone was trying to frame him.