I believe people can still be invited to attend a Police interview voluntarily even as a suspect, but in general, and certainly in cases like this, arrest seems to be the way they go. Used to be common practice for interviews to take place without solicitors present, but that seems to be a big no no now (ECHR based court decisions etc) unless the suspect specifically decides they do not want one present. I would imagine Police Scotland will have wanted a high profil;e case like this done by the book namely arrest and a caution and interview with the suspects legal team present. I'd think the cops investigating will ultimately submit a report to the Crown Office for their (the Crown Office) decision re charges etc. Then the fun will begin!!