It really depends on why the government took the funds. Drug related? Insurance fraud? Ponzi scheme?
I can't answer that for you, but there are a lot of reasons and if they suspect the money was illegitimate, at that amount you are looking at a felony charge.
Get a copy of the will and/or the insurance policy. A death certificate. Bank statements from your mother showing the insurance deposit, and showing the transfer to you.
You need documentation to show that you believe the money was legitimate, and you need a lawyer.
If there is the slightest doubt in your mind that any of this money could be from something shady, tell your lawyer.