  Ru$_{2-x}$Fe$_x$CrSi ( 0 $<$ x $<$1) system is theoretically predicted to be
one of the very few known examples of robust half-metallic ferromagnet with
100\% spin polarization. Since Cr is considered to be the main contributor to
magnetism, the Fe/Ru substitution is not expected to disturb its magnetic
properties any significantly, and hence all Fe-containing members of the series
are predicted to follow Slater-Pauling rule with a saturation magnetic moment
of 2 ${\mu_B}$/f.u. However, contrarily to the theoretical expectations, some
experiments rather show a linear variation of the saturation magnetization and
Curie temperature with Fe (\textit{x}) substitution. The equiatomic member
FeRuCrSi of this family is also considered as a technologically important
material, where the band structure calculations suggest the material to be spin
gapless semiconductor. Through our in-depth structural analysis of FeRuCrSi
using X-ray diffraction, extended X-ray absorption fine structure and $^{57}$Fe
M\"{o}ssbauer spectrometry, we found a random disorder between Fe and Ru sites,
while the magnetic moment in this system is actually contributed by Fe atoms,
questioning the very basic foundation of the half-metallic character proposed
by all theoretical calculations on Ru$_{2-x}$Fe$_x$CrSi series. Our
M\"{o}ssbauer result also envisions a rather rare scenario where the main
physical properties are intricately correlated to the chemistry of the material
in the form of random atomic disorder on a localised scale.
