Sounds a bit naive but I read somewhere that neutrinos were thought to account for dark matter to an extent and I think Zwicki came up with the idea before cosmic rays were announced (not sure though). Any help would be great.
It is highly unlikely. Neutrinos are known to account for a small part. The problem with neutrinos is that they are low mass and usually highly relativistic. DM needs to be made up of particles or objects that are slow and non relativistic. DM concentrates around galaxies, and tends to stay around, DM needs to be cold to stay around.
As for cosmic rays it's even worse. They are basically highly relativistic protons, also certainly not cold. They also electromagnetically interact, it is known that DM interacts little (eg when a galaxy goes through another the DM is hardly affected). Charged particles could not do that.
The best remaining idea on DM is that they are unknown WIMPS, weakly interacting,massive particles. The problem is of course we still don't know what those may be. Black holes, small or medium sized, were also considered and they would have to be Early universe remnants, calculations are also that they just can't be a significant percentage of DM.
Some ssuperparticles were also considered, but with no light superparticles found at LHC people are looking for other alternatives.
So, don't know but unlikely any of those.