  This work has attempted to reconcile puzzling neutrino oscillation results
from the LSND, KARMEN and MiniBooNE experiments. We show that the LSND evidence
for $\bar{\nu}_\mu \to \bar{\nu}_e$ oscillations, its long-standing
disagreement with the results from KARMEN, and the anomalous event excess
observed by MiniBooNE in $\nu_\mu$ and $\bar{\nu}_\mu$ data could all be
explained by the existence of a heavy sterile neutrino ($\nu_h$). All these
results are found to be consistent with each other assuming that the $\nu_h$ is
created in $\nu_\mu$ neutral-current interactions and decays radiatively into a
photon and a light neutrino. Assuming the $\nu_h$ is produced through mixing
with $\nu_\mu$, the combined analysis of the LSND and MiniBooNe excess events
suggests that the $\nu_h$ mass is in the range from 40 to 80 MeV, the mixing
strength is $|U_{\mu h}|^2 \simeq 10^{-3}-10^{-2}$, and the lifetime is
$\tau_{\nu_h} \lesssim 10^{-9}$ s. Surprisingly, this LSND-MiniBooNE parameters
window is found to be unconstrained by the results from the most sensitive
experiments searching for heavy neutrino. We set new limits on $|U_{\mu h}|^2$
for the LSND-MiniBooNE favorable mass region from the precision measurements of
the Michel spectrum by the TWIST experiment. The results obtained provide a
strong motivation for a sensitive search for the $\nu_h$ in a near future $ K$
decay or neutrino experiments, which fit well in the existing/planned
experimental programs at CERN or FNAL. The question of whether the heavy
neutrino is Dirac or Majorana particle is briefly discussed.
