  We present hybrid spectral energy distributions, combining photon and
neutrino fluxes, for a sample of blazars, which are candidate IceCube neutrino
sources. We furthermore check for differences in our sources' variability in
the near-infrared, optical, X-ray and $\gamma$-ray bands compared to a sample
of non-neutrino source candidate blazars, and investigate the state of each
blazar at the arrival time of high-energy neutrinos. We find no significant
differences when comparing our sample with control sources, also in terms of
their spectral energy distributions, and no correlation between flaring states
and neutrino arrival times. Looking for signatures of hadronic production, we
check for similar strengths of the $\gamma$-ray and neutrino fluxes and find a
$2.2\,\sigma$ signal for our source candidates. The hybrid spectral energy
distributions assembled here will form the basis of the next step of our
project, namely lepto-hadronic modelling of these blazars to assess the
physical likelihood of a neutrino connection.
