Your "smoking knife" illustration notwitstanding, otto, in both the DNA snatch setup and the friendly cellmate scenarios, I've never been quite sure where the boundary lies between legitimate sting and illegitimate entrapment. Often seems kinda fuzzy, if you ask me. MOO. Again "tunnel vision" is a well understood aspect of criminal investigation, or so I understand (with lots of google search support) so it's actually not true that talking and walking like a duck identifies one as a duck. The quacker could actually be a child's toy; a kid in a Halloween costume; a robot; a remote controlled bomb - or really lots of possibilities. The fierce drive towards arresting somebody is, I think, especially prone to investigative errors, oversights and/or mistakes, accidental or otherwise, when there's a horrible crime that has garnered widespread public attention and therefore LE itself tends to feel itself to be on trial. MOO IMHO
I don't think that the police are feeling like they are on trial, or that someone is
shooting at their feet regarding solving murders. They follow the evidence. In this case, in the period of two weeks, the evidence led investigators from the crime scene, to the truck, to the truck's owner, to the Airdrie property, to fast tracking forensics, arrest, and the laying of charges. If police made assumptions or jumped the gun, at what step did that happen?
Counter-examples to the belief that police make quick arrests due to "feeling they are on trial" are high profile cases that go cold. The murder of an RCMP officer is high profile.
"On December 13th 1997, 52-year-old Peter Sopow and his 47-year-old girlfriend, Lorraine McNab, were shot to death on her acreage just south of Pincher Creek. The victims were ambushed and shot outside and their bodies were then dragged into a horse trailer on the property. The bodies were found in that locked horse trailer just before noon on December 15th.
Sopow, a 32-year veteran of the RCMP at the time of his death, was the father of two grown children, and a Sergeant with the Fort Macleod detachment.
McNab was a kindergarten teacher at Canyon School in Pincher Creek and was the mother of two teenaged children. She and Sopow were both divorced and had been dating for about six months.
http://www.country95.fm/news.asp?ID=7835
Jane Johnson appears to come from a prominent family, also high profile.
"Jane JOHNSON and her daughter Cathryn were murdered in their home on the evening of September 3rd, 1996. The culprit(s) set fire to the residence in an effort to conceal the crime.
It is believed that this was not a chance or random act perpetrated by someone committing a break-in or an assault as evidence gathered does not support this. Further, it is believed the killer(s) knew the victims and were aware of their day-to-day patterns."
http://www.rcmp-grc.gc.ca/cc-afn/johnson-jane-cathryn-eng.htm
It seems that if police make an arrest in two weeks, they are jumping the gun, but if the case goes cold, they are incompetent. What is the correct amount of time for an arrest to be made such that the community has confidence in the abilities of investigators and prosecutors?