The murder is not solved, and will never be solved. The Chechen security forces, de facto licensed to shoot opposition politicians, are ptetty much sure of it.
Investigators tried twice to present charges in absentia to Ruslan Geremeev, a possible organizer of the murder of Boris Nemtsov, but both times the decision wasn't signed by the head of the Russian Investigative Committee Alexander Bastrykin.
The Investigative Committee of the Russian Federation established the exact date when preparations began for the assassination of Boris Nemtsov. This happened in September, 2014. The total payment for the crime committers should have been 15 million rubles. They were ready to murder Nemtsov as early as in October, but an opportunity turned up only four months later.