Although the possible accidental release from a bioweapons program remains unlikely, the finding of a "natural" version of SARS coronavirus in 2 (and possibly many more) species in China, makes an accidental release of a lethal mutant a more likely possibility.
The vast majority of SARS isolates from patients have a 29 nt deletion, which is the type of change that could be man-made. However, although it still seems rather unlikely, the identification of several animal isolates, and one human isolate, GZ01, with the 29 nt present, changes the bioterror odds somewhat.