  We present the results of the X-ray spectral analysis of the deep survey
obtained with the XMM-Newton observatory on the Lockman Hole. The X-ray data
and the cumulative source counts were reported by Hasinger et al. (2001). Our
sample contains 104 sources with a count limit of 70 of which 55 have redshift
identification. The redshift distribution peaks at z ~ 0.8, with a strong
excess of low z AGN and a deficiency of sources at z > 2 compared to population
synthesis models for the X-ray background. The type 2 (obscured) AGN have
weaker soft X-ray and optical fluxes. They cluster around z ~ 1. There is a
clear separation between the classical/type 1 AGN and the obscured/type 2 ones
in several diagnostics involving X-ray colour, X-ray flux, optical/near IR
colour and optical brightness. Using the z subsample, we show that this
separation between the AGN populations is a consequence of different absorption
column densities. The two populations have the same average spectral index,
Gamma ~ 1.9. At the 70 count detection limit, there is also a strong overlap
between the two populations in hard X-ray flux and near IR brightness. These
diagnostics should enable the classification of obscured/type 2 AGN very faint
optically.
