My ex-husband recently died of cyanide poisoning and it is believed that his wife was involved in his death; this is under investigation by the proper authorities at this time. The property he purchased 32 years ago when we were together was supposed to be our daughter's inheritance. He had a will which came up missing when he mysteriously died and now his wife is selling the property for $250,000. Can we legally contest the sale?

You can not contest, but the daughter can, she needs to search out any possible lawyer he may have used to see if a will can be found.

At a minimum if the home is sold the money needs to go into an escrow account and frozen pending the outcome of the investigation. Depending on location the ex wife may be entitled to a portion of the sale money. But there is also laws on the book that persons can not profit from the commission of a crime.

Unless there is a valid Will bequeathing the property to your daughter it goes to his wife in MOST States. We need to know where you are.

A promise to leave something to someone means nothing if it's not in writing. Was this EVER contained in a Will?

It's entirely possible the Will was rewritten and the property left to the wife.

And I agree - if the wife had anything to do with his death and the authorities can prove it, she's out of the picture.

EDIT: You appear to know there was a Will because you state it's now missing. Contact the Attorney who prepared it and see where the original Will is filed. The Attorney may have it, Probate Court (or something similar may have it) OR your "ex" may have taken it with him.