I agree that he used his daughters on Mothers Day. Not nice.
I think if he had harmed her before Mothers Day, and if people were inquiring about Suzanne not returning calls, missing her, to which he had no good answers to give, and BM couldn't take it any more.
He had to slap together a plan so people would stop bothering him. He needed Suzanne to be officially missing. He desperately needed the staged bike to be discovered that day so he could come home and not have to answer personally to anyone looking for Suzanne.
BBM:
I firmly believe SM came to harm before Mother's Day.
If she was killed on either Friday or Saturday, the issue of people trying to reach SM via phone that weekend would have presented the perp with a real conundrum. What to do?
Ignore the call and/or texts, and possibly set off alarm bells before you were safely away from the scene?
Respond via text as SM, and hope that you sounded like SM?
Respond as yourself, and indicate that SM was off doing something, but that you'd give her the message they called?
I'm reminded of the Kelsey Berreth case, and her moronic killer's attempts to pass himself off as her in text messages he sent to her employer and her mother.
Her mother definitely thought there was something off with the messages, as they didn't read the way Kelsey normally corresponded…which makes sense, because Kelsey was bright, and literate, whereas her killer is neither.
I'm thinking any attempts made by the perp here to reply via text as if they were SM would similarly read "false."
I also think that if someone provided callers with excuses for why SM wasn't around to talk, those explanations would now ring pretty hollow in retrospect, given the circumstances.
One of the things I'm curious about is whether or not her phone was "left at the house" (cough, cough) when she "went on her bike ride" (wheeze, snort), whether it was one of the items LE found, or whether her phone is currently missing.
JMO.