I don't have him down as a psychic.....
Someone could arrange such a horrible job in advance with an offender. The offender doesn't have to be psychic.
I think going back to a sexual motive there are several scenarios to consider:
1. Predatory paedophile. Though if this was the case I would have expected her body to have been found.
2. Trafficking a child into the sex trade. This would be rare given MM's age and also unlikely because she was a UK tourist and so such an abduction would invite much attention
3.
If there was parental involvement in MM's death then it's hard to explain why an accident would be concealed. The threat of a "neglect" charge surely wouldn't have been deemed to subsequently lead to a prison sentence especially given the family's connections to people in high places. If they had given MM an over the counter antihistamine (as a sleep aid) then this wouldn't have led to a prison sentence even when combined with alleged "neglect". However if there was some evidence of sexual abuse then that would provide a higher likelihood of the need (motive) to cover up an accident.
All three of the above are pure speculation and just ideas exploring possible sexual motive scenarios. I am not suggesting that there is any evidence that MM was killed by a predatory paedophile nor the victim of sexual abuse carried out by anyone in her family or their friends. Also the parents are quite rightly legally presumed innocent of any involvement in her dissappearance.