And since he saved everything to cloud and has already agreed to turn the materials over to US authority at the proper time, he should not only receive an immune agreement but a sizeable award !
I am not a cop and do not play a cop on TV but note that on NCIS and CSI a person can be detained as a material witness.
Perhaps Guccifer is cooling his heals as a material witness. His efforts and testimony are germane to the case along with his evidence