Yep, it would seem to be an admission of guilt. BUT, if evidence is not in his favor, and it's looking like the jury will convict, then I think saving his neck would be more important - haven't there been cases where the accused is innocent, the evidence is shaky, yet the jury convicts anyway? If he is guilty, then that's different.
I put myself in Westerfields place. IF I were NOT GUILTY, then I would take my chances before saying I was, even if the death penalty was a possibility.
IF he says "guilty", he's a dead man walking even if he gets "life" without parole.
I would hope, if he cops a plea, that he would have to "confess" to exactly how he committed the crime, and then we would have no doubt he really did do it, if that makes any sense.
sw