Is this realistic? Can a ninja star penetrate and be accurate enough to kill a person?
The question has been recently clarified to be whether shuriken could kill, rather than whether they were historically used to kill.
This issue was looked at in a German study that was looking for evidence on whether to support a ban on modern variants.
- Kettner M, Gade G, Ramsthaler F, Shah S, Pape A, Theisen A, Schmidt P., Experimental studies on the wounding capacity of recently developed shuriken/throwing stars and their legal categorization--an interdisciplinary view Arch Kriminol. 2010 May-Jun;225(5-6):167-80.
While the focus was on plastic and "cyclone" shuriken, they also looked at three "traditional metal shuriken with blunt edges and peaks produced for decorative purposes." I think it is safe to assume that traditional combat shuriken would be at least as effective than traditional decorative ones, so the results can be extrapolated.
The abstract explains that the experiment was done on "human skin" (presumably a cadaver), and compared it against modern shuriken that were tested against pig carcasses. The traditional shuriken were thrown from a distance of 2m by an experienced thrower.
Traditional shuriken were less effective at penetrating human skin than modern variants were at penetrating pig skin. However, the damage inflicted wasn't trivial.
[traditional] shuriken yielded maximal penetration depths between 0.9 and 2.3 cm.
I hope it is clear that a 2cm deep stab wound could be insignificant or fatal, depending on what part of the body is hit. The study authors seem to agree:
This study indicates that all three types of shuriken may inflict lethal wounds upon opponents in close combat.
While it is irrelevant to this discussion, this study struck me as poorly controlled. Why are they comparing damage done by a cyclone shuriken to pig skin from 4 metres, to damage done by a traditional shuriken to a human skin from 2 metres? Why not do both experiments against pig carcasses from the same distance?