Suppose A is a compact normal operator on a Hilbert space H with certain lacunarity condition on the spectrum (which means, in particular, that its eigenvalues go to zero exponentially fast), and let L be its rank one perturbation. We show that either infinitely many moment equalities hold or the linear span of root vectors of L, corresponding to non-zero eigenvalues, is of finite codimension in H. In contrast to classical results, we do not assume the perturbation to be weak. M.S.C.(2000): Primary: 42A65; Secondary: 42C30 Keywords: selfadjoint operator, rank one perturbation, completeness of eigenvectors, Pólya peaks n |s n | −k | P n a, b | < ∞, but the equality (M k ) does not hold. Then L and L * are nearly complete.Moreover, for any ε > 0 there is a radius r > 0 such that the intersection of the non-zero spectrum σ(L) \ {0} with the disc B(0, r) is contained in the union of angles α ℓ − ε < arg z < α ℓ + ε, 1 ≤ ℓ ≤ n.