What has happened with the investigation of mtgox.com? Why hasn't there been any update since 9th of September 2015? What has happened since then?
AFAIK, the latest official news is the article After the CEO’s Indictment the Great Mt. Gox Bitcoin Mystery Deepens from the 14th of September 2015, and these two tweets:


  PDG #Français de MtGox,banque #BTC basé à #Tokyo sera condamné sans jugement sur des charges n'ayant aucun lien avec disparition 50,000,000$ – @NathalieStucker (Jan 7th 2016)


and


  30歳のフランス人が6ヶ月間以上東京の #刑務所 に #永遠 と取調べられてるため、#外国メディア は日本の #司法制度 に #疑問。23日間の #保管期間、#人権 にかかわる。– @NathalieStucker (Jan 9th 2016)


You can follow Nathalie Stucky on Twitter @NathalieStucker and as a contributor on Daily Beast, she seems to be the only one interested in truth and justice on this topic.

Now a few unofficial news, AFAIK Mark Karpelès hasn't been allowed any visits, not even contacts with his family and is not allowed to use a computer either. 
 He already lost 35 kg but still hasn't accepted to be the scapegoat, which seems to be why he's still detained after more than 4 months, without any trial or official charges…