Squid are certainly capable of killing a human. The smaller Humbolt squid are definitely known to attack people, there are also reports of fatalities. Fishermen in the Sea of Cortez are particularly wary of these creatures which are reported to on occasion reach sizes of 12 foot.
I can’t remember the name of the programme but a film crew did get pictures of a squid which was speculated to be a giant Humbolt. Supporting the possibility of this in ‘Man Eaters’ by Micheal Bright (
http://www.randomhouse.co.uk/authors/michael-bright) there is a report of an example being caught which measured 45’.
The giant squid attacking the survivors is also mentioned in ‘Man Eaters’ as well as in ‘Invitation to Oceanography’ (huge url but can be found on Google books), Bright writes;
the British troopship Bitannia was sunk by the German surface raider the Santa Cruz in mid Atlantic. Ashe was about 1,200 miles west of Freetown. Some men survived and clung to floating spars and life-rafts. Lieutenant
R.E.G. Cox and eleven other men were supported by a very small raft; only their heads and shoulders were above water. Sharks were the number one fear, but one night something far more sinister came up from the depths. A giant squid surfaced and wrapped a tentacle around one sailor and pulled him under. A little later Cox was seized by the leg, but the beast let go. Cox recalls incredible pain as the suckers were pulled off. The next day he noticed large ulcers had appeared where the suckers had gripped, and when rescued the medical orderlies were constantly treating the wounds.
Later it says;
Professor John Cloudesly Thompson at Birkbeck College University of London was allowed to examine them. He was able to confirm that they were sucker scars likely from an attack by a giant squid.
The story does seem to stand up, here;
http://www.cmbower.co.uk/Articles/Other ... annia.html
this first had account from a survivor of the sinking makes no mention of squid, but looking at the appendix of survivors this man is shown to have been on a life boat, whereas Cox is listed as being recovered from a raft as in the account, though the number of his fellow survivors is given as two not eleven. Finally further down the appendix section this note appears;
Lt R E Grinan-Cox I.A. (survivor of raft - lived in Fareham and whose harrowing story was reported in papers).
Plenty more about killer molluscs in Bright’s book and also another underwater cryptid encounter;
Neil Daniel, writing in Oceans in 1989, mentions ‘rumors of commercial divers having spotted one (giant octopus) hulking monster some 50ft in diameter in deep water off the coast of Japan’.
Also there are reference to illustrations in an 19C Japanese book called ‘Land and Sea Products’ of giant octopus being fished and their limbs for sale in markets. The fishing print can be seen here;
http://www.myjapanesehanga.com/home/art ... -1842-1894
There is also an account of a giant octopus overturning a catamaran of the Philippines in 1989.
Regarding the man being eaten by a car-sized grouper, it seems they might have been a lot bigger in the old days:
That is fascinating, I’ve got a long term interest in Roman art and can recall a fresco which shows two men in a small boat surrounded by giant or at least disproportionately large fish, I just thought at the time that proportions weren’t important in what they were trying to convey. I’m still not convinced this isn’t the case as the greater sizes shown weren’t restricted to groupers.