  We present a strong hint of a connection between high energy $\gamma$-ray
emitting blazars, very high energy neutrinos, and ultra high energy cosmic
rays. We first identify potential hadronic sources by filtering $\gamma$-ray
emitters %from existing catalogs that are in spatial coincidence with the high
energy neutrinos detected by IceCube. The neutrino filtered $\gamma$-ray
emitters are then correlated with the ultra high energy cosmic rays from the
Pierre Auger Observatory and the Telescope Array by scanning in $\gamma$-ray
flux ($F_{\gamma}$) and angular separation ($\theta$) between sources and
cosmic rays. A maximal excess of 80 cosmic rays (42.5 expected) is found at
$\theta\leq10^{\circ}$ from the neutrino filtered $\gamma$-ray emitters
selected from the second hard {\it Fermi}-LAT catalogue (2FHL) and for
$F_\gamma\left(>50\:\mathrm{GeV}\right)\geq1.8\times10^{-11}\:\mathrm{ph}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$.
The probability for this to happen is $2.4 \times 10^{-5}$, which translates to
$\sim 2.4 \times 10^{-3}$ after compensation for all the considered trials. No
excess of cosmic rays is instead observed for the complement sample of
$\gamma$-ray emitters (i.e. not in spatial connection with IceCube neutrinos).
A likelihood ratio test comparing the connection between the neutrino filtered
and the complement source samples with the cosmic rays favours a connection
between neutrino filtered emitters and cosmic rays with a probability of
$\sim1.8\times10^{-3}$ ($2.9\sigma)$ after compensation for all the considered
trials. The neutrino filtered $\gamma$-ray sources that make up the cosmic rays
excess are blazars of the high synchrotron peak type. More statistics is needed
to further investigate these sources as candidate cosmic ray and neutrino
emitters.
