On finite groups isospectral to $U_3(3)$

The spectrum of a finite group is the set of all its element orders. A finite group $G$ is calledcritical with respect to a subset $\omega$ of natural numbers, if $\omega$ coincides with the spectrum of $G$ and does not coincide with the spectrum of any proper section of $G$. We study the structure of groups isospectral to a simple unitary group $PSU(3,3)$. In particular, we give a description of the finite groups critical with respect to the spectrum of $PSU(3,3)$