We present a detailed investigation of structural properties of manganese doped strontium titanate ceramics and Verneuil grown single crystals, the last prepared with Sr deficiency compensated by proper Mn amount. EXAFS, TEM, ESR and Raman techniques, combining local and lattice probes, allows to inspect the local chemical environment and electronic structure of manganese taking into account possible chemical non-homogeneities and/or phase segregation. On the basis of experimental evidences, structural models for Mn insertion in SrTiO3 are discussed considering possibility for Mn ions to occupy both Ti4+ and Sr2+ sites as well as manganese segregation and Mn incorporation related non-homogeneities.