There is a lot of stuff spinning around in my head as I write this,
but my main thought is to let people know what (it seems) was the
cause of this accident. The main factor in this has surprised a good
number of the climbers I have talked to.
I know there has been some discussion of this on the web already.
Hopefully by telling the whole story - however irrelevant some of it
might be - all of the various questions might be answered. I will try
to reply to any questions where I can tell you something vaguely
useful.

%==== The long story [skip ahead for the facts] ====%%
On Monday we climbed the first four pitches and returned to the
ground, leaving ropes in place to jug the next day. All the anchors we
used were fixed, except maybe for the one at the top of the first
pitch.
Pitch 1 is slightly grotty 5.6 climbing. Pitch 2 is a pretty nice 5.7
flake and ends at the left end of a large sandy ledge. We fixed a 60m
rope ("the blue" 60mx10.5mm) to this anchor, having got beta saying
this would just reach the ground. Pitch 3 is a mixed bag of sandy 5.5
and ends at the base of a huge smooth clean red wall, the stuff we
came to do. We fixed "the green" (55mx10.5mm) to this anchor and
chucked it back down to the sandy ledge (top of pitch 2). Pitch 4 is
where it gets fun. I lead the pitch (C2 aid) and Ross followed,
cleaning the gear. We fixed our 60m lead rope ("the yellow"
60mx10.5mm) to this anchor and abseiled down. Then down the green to
the sandy ledge. Then down the blue (carefully checking it reached)
back to the ground. It didn't quite reach the dirt, but left us with
maybe 20ft of trivial down-shuffling to get back to our bags. We left
the 3 ropes in place and headed off for a beer.

Tuesday morning we jugged the ropes. Amongst all the other crap you
take aid climbing, we had a 9mm rope. We planned to lead on the yellow
(the top fixed rope) and take the 9mm to deal with the double-rope
abseils on the descent. We would chuck the green down to the big sandy
ledge as we went past it, and then could retrieve the green and the
blue by jugging just the blue on Wednesday and abseiling down.

I set off first, Ross followed. I got to the top of pitch 4 as Ross
arrived at the top of pitch 3. Ross had got some two-way radios
earlier on the trip and we chatted on the radio: the weather forecast
had been slowly deteriorating for the last 3 days, today was 50%
chance of afternoon rain, there were a lot of gloomy clouds brewing
above us, the sandstone is all bad in the wet, we were not super fast
aid climbers...there were a lot of reasons for continuing, mostly that
I didn't want to have to lead that C2 pitch again!! A brief spot of
rain actually hit us and we decided to bail.
I pulled up the 9mm rope, tied it to the yellow, stripped the anchor
and descended to the top of pitch 3. Meantime Ross had been untying
the green from this anchor and getting ready to set up a double-rope
abseil. I got down to him, chucked him the end of the yellow to tie to
the green and started pulling the ropes down from above.

Ross headed off down to the big sandy ledge as I coiled the 9mm and
put it on my back. He radioed me to say "rope free" and I headed down.
I arrived on the big sandy ledge about 10-15ft away from the anchor -
Ross was off to my left, already clipped into the anchor and sorting
out the blue rope, ready to set up the last abseil. I chucked the
loose end of the yellow to Ross and started pulling the ropes from
above. I was unclipped at this point - being a very bad boy, even
though it was a huge ledge. This was actually the only thing that
struck me as unsafe about our whole day. As the knot came down, I
stopped and untied it to free the yellow, which was now all tangled up
in plants and rocks on the ledge. Ross fed it over the edge as I
untangled it from everything on the ledge. I started pulling the green
down as Ross sorted himself out over at the anchor. I was coiling the
green rope as Ross called over to say "see you at the bottom in a few
minutes", he saw me coiling the green and offered to carry it, since I
had the 9mm already on my back, but he already had our daysack on so I
said I was fine taking it down. I turned to just finish up coiling the
green and at that moment he fell.

I rushed over and there was nothing there - our ropes had gone, Ross
had gone, the anchor was fine, untouched. Everything floated for a
moment, slipped sideways and turned unreal - then I started
shouting...I knew I had to get down in case by some impossible chance
there was something I could do to help him. I was yelling down to the
road and got someone's attention, they flagged down one of the shuttle
buses and shouted that help was coming. I had the 55m green and the
50mx9mm ropes with me. I couldn't get to the ground in one go but I
knew there was another anchor (top of the Alpine Start for those that
know it) that I would be able to reach. I set up the double rope
abseil and set off down. The ropes tangled around everything - it was
a complete shambles. I saw the rangers and the ambulance arrive; the
rangers were racing up the hill to Ross. I set up the second abseil,
it was all taking so long...as I reached the ground one of the rangers
came over to tell me what I already knew.

%%==== Some stuff that I do know ====%%
Ross was found with the two ropes correctly through his belay device.
The ropes extended about 10feet "above" him (the other 190feet being
"below" his belay device) and the ends were not tied together.
Throughout this trip we had always been tying ropes together using a
fig-eight knot (more below).
The only other abseil Ross set up that same day (from top of pitch 3
down to the big ledge) he had used the fig-eight knot with no back up
knot on the tails. The knot was neat, I don't remember exactly how
long the tails were but they didn't cause me a second glance.
I could not see exactly what Ross was setting up on that last abseil -
he was 10ft or so to my left and was sitting (while clipped in) so
that he obscured my view of the anchor.

The fig-eight I refer to is tied as follows: The two ends you want to
join are held parallel with the ends "pointing" in the same direction.
You grab both ropes together and then tie a regular single fig-eight
knot in both ropes at once.
What we did NOT use: The only other way that might be confused is when
you have the ends pointing in opposite directions. Tie a single
fig-eight in one rope then follow this through with the other rope -
we did NOT do this.

%%==== The important bit ====%%
Some guys that were helping me out played around in their yard with
this fig-eight method, tying it and trying to pull the knot apart.
They found some worrying things.
-The way the ropes pull on this knot on a double-rope abseil deforms
the knot badly.
-If the knot is not perfectly "dressed", in particular if there is a
single slack loop anywhere on the fig-eight, they could pull the knot
through even with 6 INCHES of tails, just pulling the ropes apart as
happens naturally on an abseil. 6 inches of tails is NOT ENOUGH. If
you use this knot, tie a back up knot and leave LONG tails. It scares
me to think that I could have innocently/ignorantly made this same
catastrophic mistake.

%%==== My thoughts (not facts) ====%%
The only plausible explanation of this accident I have come up with is
that the knot slipped off the ends. I won't go through all the
alternate scenarios and my objections to them here. I hope it doesn't
sound contradictory to say that Ross was a safe climber. I never saw
him rig a belay that I thought was unsafe, never saw him do anything
that made me think "does he realise that's pretty dodgy".
We were not in a big rush getting down. We were moving quickly and
efficiently but with no sense of panic or anything like that.
Ross knew that the last abseil was a long one and we would be a bit
tight on rope. I can imagine that would make him want to keep the knot
pretty near the ends, but I do not believe he would only leave
something ridiculous like one inch of tails. I think he must have tied
the knot with something like 6inches of tails, thinking this was
plenty (go tie the knot - it looks good with this much rope sticking
out of it) and maybe he didn't make it all neat and snug. I think when
he set off he was happy with his set-up, not thinking at all that the
tails were dangerously short.
The first 30feet of this abseil are a little slabby - and with two 60m
ropes you do have to feed armfuls through your belay device at the top
- the first few feet of such an abseil are always a bit jerky. I guess
he fed through a couple of armfuls of rope and hence bounced the knot
just a couple of times, which caused it to fail.

While I will never know for sure what happened, I do know what any of
you can prove to yourselves - that you can get this knot to fail even
with 6 inches of tails. I did not know that the necessary margin for
safety was so wide for this knot, I am sure Ross did not realise this
either.

The ropes involved (the blue and yellow) have been sent to one of the
testing guys at Black Diamond who is going to run some relevant tests
involving this fig-eight knot. I will post anything they find that
might be of interest.

%%==== Last words ====%%
Thoughts of Ross are vividly etched in the minds of almost everyone he
met. We miss him terribly.
The only other thing I want to say here is that the Rangers at Zion
were incredible; the way they dealt with the incident, the diligence
of their investigation and the compassion that they showed me...I have
only praise for everything they did. I was overwhelmed by the
generosity of so many other people in Springdale - it's a small town
of wonderful people. Despite everything, I have some very fond
memories of Zion and the people I met.
It is a beautiful place - you should go there and climb those amazing
walls.