San Diego's homeless population is on edge after four attacks on transients in four days, two of them fatal.

Police are seeking someone they now identify as the sole suspect, a man seen on convenience store surveillance video wearing a cap, jacket and backpack.

In the latest of the attacks, a 23-year-old man was seriously injured Wednesday and is not expected to survive his upper-body injuries after being attacked.

A news release said the latest victim was set on fire, though Capt. David Nisleit said earlier that a witness pulled away a burning cloth that the attacker had placed on the victim before fleeing.

As in previous attacks the victim was sleeping in the early morning hours when the assailant approached.