Mark Karpelès, the head of collapsed bitcoin exchange Mt. Gox, spoke to The Wall Street Journal's Takashi Mochizuki and Eleanor Warnock on Thursday night in his home on the top floor of a 33-story building in Tokyo's Meguro neighborhood. It was his first media interview since a news conference when Mt. Gox filed for bankruptcy in February. Here are some excerpts:

Q: What are you working on lately?

A:...