Consider an expression of the following form:
$$I^{\mu\nu}(r) = \int d^{3}k\ \ d^{3}l\ \ \delta^{4}(r-k-l)\ (g^{\mu\nu}k\cdot{l}+k^{\nu}k^{\mu}-k^{\mu}l^{\nu})$$
$I^{\mu\nu}$ must be of the form
$$I^{\mu\nu}(r) = Ar^{\mu}r^{\nu} + B\eta^{\mu\nu},$$
where $A$ and $B$ are constants.
How can you determine this tensorial form of $I^{\mu\nu}$?