Hojjat al-Islam Seyyed Mahmoud Du’ei once explained through a series of memoirs that the Shah regime had become scared of the incresing popularity of Mostafa Khomeiniamong public masses.
That is why the regime had first imprisoned the eldest son of Imam, but seeing enormous reaction by the public released him and then sent him into exile to join Imam in the Turkish city of Bursa.
Then the Shah regime in an aplogistic manner explained that since Imam was alone in Turkey and needed company of his eldest son.
But actually, the regime had felt that the presence of Mostafa Khomeini in Iran could accelerate the struggle for the Islamic revolution and could result in an earlier fall down of the Shah and his associates.
Extracted from a collection of memoirs about Imam