0 berger is saying. it s an investigation and international, and we re really good at this. the fbi is very good working with our other agencies. there are persons of interest in the united states. we re looking at phone calls before and after the bombing. this type of investigation. let s go to boston. nbc s michelle franzen. a good sunday to you, my friend. new information about the suspects and their mother. reporter: yeah, again we re learning more, alex, more overseas and also here at home. as you heard earlier, u.s. officials tell nbc news that they are focussing on leads here at home and also overseas. authorities have been operating under the theory that the suspects acted alone, but at the same time saying they are not ruling anything out. investigators say they are still looking into all possibilities in the boston bombing case, including tracking possible leads on the two bombing suspects here at home and overseas. authorities confirm the brothers mother was placed on