Amnesty (from the Greek amnestia, oblivion)is to overlook and forgive and FORGET crimes done.
a - neagtive
manas - to think, to mind
taya - 'ness', 'tion' kind of suffix to make something into adjective. "s" usually conjoins "t" as part of Sandhi rules (Euophonics Rules), and suffix 'ya" carries the sense of English Adverb carried by suffix 'y'. Sanskrit Adverbs are almost missing except for some suffixes and gerunds. This is not that simple as in Sanskrit 'y' is a very overloaded letter with many rules. "tavya" is for Potential Participle (besides 'y'), "tvaa" is for Gerund (besides 'y'), and "tva" is for "ness". "tya" is also used as Aggregative Noun as part of Numeral Adverbs. So here this may refelect a collective process, which is Amnesty more about.
a-manas-taya - the act of making something unthinkable - made into oblivion.
a-manas-sya-ti - that shall be thought not - made unconsidered.
a-manas-taya - not to think