My reading of the SEC/CFTC report is pretty much the opposite of "absolved", though they consider HFTs only one factor magnifying the spike, rather than the initial cause (i.e., consider HFTs a volatility-increasing factor).

From the report's punchline:

The combined selling pressure from the Sell Algorithm, HFTs and other traders drove the price of the E-Mini down approximately 3% in just four minutes from the beginning of 2:41 p.m. through the end of 2:44 p.m. ... HFTs began to quickly buy and then resell contracts to each other – generating a “hot-potato” volume effect as the same positions were rapidly passed back and forth. Between 2:45:13 and 2:45:27, HFTs traded over 27,000 contracts, which accounted for about 49 percent of the total trading volume, while buying only about 200 additional contracts net.