Asking for your Social Sec # is odd, and probably illegal. But as one who has been the official witness of record for countless crimes, I say give the cop a bye on this. He may have not trusted you as a witness, and was fishing for info to confirm you are who you say you are. Happens all the time [not much to me, since I'm usually in work garb], and though it may have irked you, some sort of outside verification or questioning is SOP when the officer is in doubt.
Doesn't make it right, but I can understand it.
