Starmer failed to take any action against Savile
How could he have?
The police made a referral (re. 4 historic abuse claims) to the CPS in late 2009.
The reviewing lawyer made a decision not to pursue charges.
The reviewing lawyer could (and should) have escalated the matter up the chain of command, which could ultimately have resulted in a refferal to the DPP, but did not.
Nobody can act on something they don't know about.
That Starmer, nor anyone else above the reviewing lawyer, was not informed of the case, has been extensively documented.
Boris Johnson, of course, made an allegation that Starmer "failed to prosecute" Saville, which was widely condemned by Tory officials as being indefensible, demand that Johnson apologize, and prompted Johnson's own policy manager to resign in protest.
All to say, the suggestion that Starmer bore any personal responsibility is widely known to be baseless, and a disgusting one to make (both for the falsity of it, and the bad-faith explotation of horrendous crimes).
Incidentally, re. "Savile was free to abuse god knows how many people as he saw fit" - there are no documented allegations of abuse after 2009.