Just caught up on this week's episode and found this thread.
I'm local to Swindon and knew lots about the case at the time.
I'm wondering if they kept the bit in about David Ainsworth commiting suicide in to show that Steve Fulcher had just lost a friend in a shocking and sudden way. Perhaps they're hinting that Steve Fulcher may have not been thinking 100% clearly. Though I completely agree that what he did was the right thing.
I thought they might mention the suicide again later on in the series or link it to something. If they don't, I think it's incredibly insensitive to David's family to just pop it in there for no apparent reason.
Wiltshire Police do not look good, and our criminal justice system is so infuriating at times. Why on earth should a murderer who pleads guilty get 5 years taken off just for admitting he did it?! I get that it's massively helpful for the victim's family to not have to go through a lengthy, painful court procedure, but I don't agree anything should be taken off the sentence 