  We carry out a systematic investigation of the total mass density profile of
massive (Mstar>2e11 Msun) early-type galaxies and its dependence on galactic
properties and host halo mass with the aid of a variety of lensing/dynamical
data and large mock galaxy catalogs. The latter are produced via semi-empirical
models that, by design, are based on just a few basic input assumptions.
Galaxies, with measured stellar masses, effective radii and S\'{e}rsic indices,
are assigned, via abundance matching relations, host dark matter halos
characterized by a typical LCDM profile. Our main results are as follows: (i)
In line with observational evidence, our semi-empirical models naturally
predict that the total, mass-weighted density slope at the effective radius
gamma' is not universal, steepening for more compact and/or massive galaxies,
but flattening with increasing host halo mass. (ii) Models characterized by a
Salpeter or variable initial mass function and uncontracted dark matter
profiles are in good agreement with the data, while a Chabrier initial mass
function and/or adiabatic contractions/expansions of the dark matter halos are
highly disfavored. (iii) Currently available data on the mass density profiles
of very massive galaxies (Mstar>1e12 Msun), with Mhalo>3e14 Msun, favor instead
models with a stellar profile flatter than a S\'{e}rsic one in the very inner
regions (r<3-5 kpc), and a cored NFW or Einasto dark matter profile with median
halo concentration a factor of ~2 or <1.3, respectively, higher than those
typically predicted by N-body numerical simulations.
