  We study the resonant contributions in the process $\bar{B}^0\to K^-
\pi^+\mu^+\mu^-$ with the $K^-\pi^+$ invariant mass square $m_{K\pi}^2\in [1,
5] {\rm GeV}^2$. Width effects of the involved strange mesons, $K^*(1410),
K_0^*(1430), K_2^*(1430), K^*(1680), K_3^*(1780)$ and $K_4^*(2045)$, are
incorporated. In terms of the helicity amplitudes, we derive a compact form for
the full angular distributions, through which the branching ratios,
forward-backward asymmetries and polarizations are attained. We propose that
the uncertainties in the $B\to K^*_J$ form factors can be pinned down by the
measurements of a set of SU(3)-related processes. Using results from the large
energy limit, we derive the dependence of branching fractions on the
$m_{K\pi}$, and find that the $K^*_2(1430)$ resonance has a clear signature, in
particular, in the transverse polarizations.
