Possible theory.... Adam says he hadn't seen Zahra since Thursday.
Police said they believe mattress was tossed approx 2 days before her disappearance. ( i don't have link handy but it was posted several times in MSM)
Perhaps EB had AB toss the mattress and he didn't even know ? OR she just told him she got a new one and tossed the other herself (with help from someone ????)
He reported to LE that they (she? he ?) disposed of the mattress, that caused the mattress getting taken from his home (to see if Zahra's DNA was on it). Search was called off that weekend..... while DNA results and tests of the mattress in the house were processed. Mattress came back negative for Zahra's DNA .... hence the start of the landfill search.
EB realizes they are on to her, at the advise of lawyer decides to help them find the mattress .... and try to implicate AB ????