That samurai committed suicide.
President Koichi reiterated Tofugu's strong and wholehearted support for our right to self-determination.
He was depressed during his imprisonment and committed suicide.
When you decide with your self, that is your own decision. That comes from you. That comes from your self determination. But the word is mainly used in Japan as a euphemism for suicide. It's kind of important that you know that.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.