Leinders was recommended to him by a member of his team staff, Stefan de Jongh, who had been doped by Leinders whilst a rider in Rabobank. Michael Rasmussen was doped by him too, and Rasmussen revealed that Leinders ran the doping programme.
Funnily enough, as soon as Leinders was appointed (on a 'consultancy' basis) Froome went from mid-pack nobody to greatest GT rider of generation and Sky went from being nowhere to a non-stop GT winning team (bar Froome's crash out in '14)
I'm sure it's just coincidence.
Leinders was given a lifetime ban 3 years ago as it was deemed he had:
"“possessed, trafficked, and administered banned performance enhancing substances and methods without any legitimate medical need, including EPO, blood transfusion paraphernalia, testosterone, insulin, DHEA, LH and corticosteroids to athletes under his care, and was complicit in other anti-doping rule violations.”