  We present a comprehensive comparative high resolution mid-IR spectroscopic
and X-ray imaging investigation of LINERs using archival observations from the
ISO-SWS and the Chandra Advanced CCD Imaging Spectrometer. Although the sample
is heterogenous and incomplete, this is the first comprehensive study of the
mid-infrared fine structure line emission of LINERs. These results have been
compared with similar observations of starburst galaxies and AGN. We find that
LINERs very clearly fall between starbursts and AGN in their mid-IR fine
structure line spectra, showing L_[OIV]26um/L_FIR and
L_[OIV]26um/L_[NeII]12.8um ratios, both measures of the dominant nuclear energy
source in dust-enshrouded galaxies, intermediate between those of AGN and
starbursts. Chandra imaging observations of the LINERs reveal hard nuclear
point sources morphologically consistent with AGN in most (67%) of the sample,
with a clear trend with IR-brightness. Most LINERs that show a single dominant
hard compact X-ray core are IR-faint ((L_FIR/L_B < 1), whereas most LINERs that
show scattered X-ray sources are IR-bright. A comparative X-ray/mid-IR
spectroscopic investigation of LINERs reveals some puzzling results. Objects
that display strong hard nuclear X-ray cores should also display high
excitation lines in the IR. However, we find two LINERs disagree with this
expectation. The galaxy NGC 404 shows weak soft X-ray emission consistent with
a starburst but has the most prominent highest excitation mid-IR spectrum of
our entire sample. Using IR emission line diagnostics alone, this galaxy would
be classified as hosting a dominant AGN. Conversely, the IR luminous LINER NGC
6240 has an extremely luminous binary AGN as revealed by the X-rays but shows
weak IR emission lines.
