On: He went to jail for stealing someone's identity, b...

[krisoft]

> Could his father not have identified him?

Probably. That assumes that the father was still alive and of sound mind. Also assumes that the father had much contact with the son.

If they have become strangers to each other a long time ago he might not even be able to tell who is his real son, but his DNA still can provide evidence.

[stanac → krisoft]

> the two men’s lives intersected briefly in the late 1980s in Albuquerque when, prosecutors said, both men were homeless

They probably didn't have much contact since he was homeless (otherwise he wouldn't be, I guess).