Sad,
Sorry to hear of your loss, but you should have run it past all of the good people here who have a world of experience in these matters. The cardinal rule is never pay money to receive money, never, and you will be safe. Second rule, never send Western Union or use prepaid card to anyone you don't personally know. Sadly, when you recieve an unsolicited or unexpected check from an unkonwn entity, you can count on it being rubber.
Just to give you an idea how serious this problem is, people are losing millions, so you are not alone. Most of us are trusting individuals, and sadly this a weakness we all share, and the crooks and scammers know this. I received several checks like you describe, and they are all legitimate looking as the computer generated check printing software makes it easy. The scammers use to bait people into sending 10% first, now they send checks our first which shows good faith whereby victims have illusion of trust.
Now be warned, the same scammers will approach you with a recovery scam, so be careful. Most are also mad to be scammed and revenge in recouping money lost is another way people let down their guard, which the scammers also know very well. I cannot tell you how many times the same scammers will play on a persons desperation to recoup their losses only to throw more money at these pretend investigation firms, so watch out.
Good luck and health to all, Mike