That's an interesting angle. He said that he thought she was sleeping over at her friend's house, and that's why he wasn't concerned until noon the following day (July 7). Noon the following day would give him enough time to dispose of a body ... but why remove the legs? That just makes a big mess that has to be cleaned up ... unless rigor had set in and it was impossible to bend the body into a shape that fits in a suitcase or a car.
"At the time of death, a condition called "primary flaccidity" occurs. Following this, the muscles stiffen in rigor mortis. All muscles in the body are affected. Starting between
two to six hours following death, rigor mortis begins with the eyelids, neck, and jaw. ... Rigor mortis then
spreads to the other muscles within the next four to six hours, including the internal organs. The onset of rigor mortis is affected by the individual's age, sex, physical condition, and muscular build. ... Several factors also affect the progression of rigor mortis, and investigators take these into account when estimating the time of death. One such factor is the ambient temperature. When conditions are warm, the onset and pace of rigor mortis are sped up by providing a conducive environment for the metabolic processes that cause decay. Low temperatures, however, slow them down."
https://en.wikipedia.org/wiki/Rigor_mortis
If she was killed, say, between 1-2AM, she was stretched out as though sleeping and the temperature was warm (Montreal temp July 6: 28C, July 7: 30C), then six hours later, at 8AM, she could have been in full rigor mortis (cool temperatures and other conditions could mean 12 hours before full rigor mortis set in). There would have been no way to move her body in daylight except by removing her legs to make to smaller "packages" (sorry for being gruesome). The fiancée had all morning to move the body and then sound the alarm at noon.
According to the fiancée, the conversation at 1:10AM has Samantha confirming that she's having a good time, and even though she was on her way home, she apparently did not tell him that she was on her way home. He then apparently was unconcerned about her until 11 hours later.
Do we know whether her fiancée is among the family members at the site where her upper body was found? It looks like dad, and one family member who appears to be closer to Samantha's age, did not go beneath the bridge to leave flowers. Is the fiancée the man in the blue t-shirt who is sitting on the left?
link for photos:
http://www.journaldemontreal.com/2015/07/11/samantha-higgins-sa-mere-retourne-sur-les-lieux-du-drame
link for Montreal temperatures:
http://www.accuweather.com/en/ca/montreal/h2k/july-weather/56186