This is difficult to answer without more information. Since the property was the personal property of the decedent (except for the laptop of the fiancee), most likely his legal heirs do have a right to it. However, if there was a 2nd Will that named the fiancee as the beneficiary of any of the decedent's estate, then those assets can be gotten back. The police did not have the authority to allow the heirs to enter into the home to remove the assets, their role would only to have been to keep the peace. They do not make legal decisions on the validity of a Will. If the heirs took anything of the fiancee's, they can be sued for conversion, perhaps in small claims court. I would need to know what was in the 2nd Will, and if it mentioned anything about how he wanted his estate distributed. I agree with the attorney that the fiancee should not have left them in. The police were bluffing if they implied they had the authority to all the heirs to remove any assets. There would need to have been a court order for the police to enforce.
If your friend called an attorney and is represented in this matter, then your friend should be asking these questions to her lawyer. If she is not represented, the general rule is that until an executor is appointed by the court, no one has the legal authority to handle the decedent's property. In reality, that is not always practical. As for the police actions, they are certainly suspect, based on the facts, as presented. This scenario requires an in depth review between the fiancé and a probate attorney.
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She did not have to turn over the property. Your friend should consult with a probate attorney and discuss her options, including opening a probate herself and asking to be the executor of the estate.