  We present a detailed multi-wavelength analysis and interpretation of the
evolution of an M7.6 flare on October 24, 2003. The X-ray observations of the
flare taken from the RHESSI spacecraft reveal two phases of the flare
evolution. The first phase is characterized by the altitude decrease of the
X-ray looptop (LT) source for $\sim$11 minutes. Such a long duration of the
descending LT source motion is reported for the first time. The EUV loops,
located below the X-ray LT source, also undergo contraction with similar speed
($\sim$15 km s$^{-1}$) in this interval. During the second phase the two
distinct hard X-ray footpoints (FP) sources are observed which correlate well
with UV and H$\alpha$ flare ribbons. The X-ray LT source now exhibits upward
motion. The RHESSI spectra during the first phase are soft and indicative of
hot thermal emission from flaring loops with temperatures $T>25$ MK at the
early stage. On the other hand, the spectra at high energies ($\varepsilon
\gtrsim$25 keV) follow hard power laws during the second phase ($\gamma =
2.6-2.8$). We show that the observed motion of the LT and FP sources can be
understood as a consequence of three-dimensional magnetic reconnection at a
separator in the corona. During the first phase of the flare, the reconnection
releases an excess of magnetic energy related to the magnetic tensions
generated before a flare by the shear flows in the photosphere. The relaxation
of the associated magnetic shear in the corona by the reconnection process
explains the descending motion of the LT source. During the second phase, the
ordinary reconnection process dominates describing the energy release in terms
of the standard model of large eruptive flares.
