Re: Fringe 4x19 - "Letters of Transit" (Live Commentary, Spoilers)
That's a way of getting Nimoy on the show.
The thing is, earlier in the season, Walter made mention of the fact that Bell was no longer alive, though the manner of his death in this timeline was never revealed.
So if he was dead, how did he get ambered in 2015?
"We travel the world in search of what we need, and return home to find it." - George Moore