As a retired LEO and traffic homicide investigator, I have worked multi vehicle fatalities more than I care to recall, this is definitely one of the worst I have seen. The driver has a history of impaired driving and heroin use. In all probability he was driving impaired and crossed into the rider's lane. These type of investigations take time and a lot of work. More often than not a good THI will have it figured out pretty quickly, but the final official report can take time. You can count on the toxicology to take 6-8 weeks for everyone involved. The suspect will probably not speak to investigators now that he has been charged, at least not without a lawyer. Since he has been charged it is fairly safe to say he was at fault in the crash.