Blockchain analysis can only go so far, but it does reveal some parameters of the puzzle. We need access to MtGox's accounting system. With that, we'd figure it out much faster than any cybercrime police team would. We are far greater in number and experience.
You place too much faith in authority. Hiring an expert in a field who does it for the money does not compare to the power the Internet has in bringing together the top experts, and this is especially true for something like cryptocurrency.
The police can get subpoena all the internal accounting records, emails, and bank records of MtGOX and any persons they have evidence to suspect. They can get connection logs and access non-public databases of various relevant data. These things alone gives them immensurably more chances of finding the culprit than all the internet detectives put together.
A hired expert will have access to all that data. Plus he will have the obligation to work hard to get to the bottom of things and avoid half-baked conclusions, PLUS he will not have to fear being sued by the people he finds evidence against, PLUS he will not be easily bribed by guilty parties. (Soon after the MtGOX database leak, a website came up that posted some tantalising results, such as the identities of the most successful traders. The website was suddenly taken down by the author without explanation.)
I repeat my question: what useful results have the crowd detectives obtained so far, in this or in any other bitcoin scam?