LONDON, April 24 (Reuters) - Saddam Hussein's urbane spokesman and Deputy Prime Minister Tareq Aziz was in U.S. custody on Thursday, the 12th senior Iraqi official to be detained. Following is a list of those so far reported captured: April 12 - AMER HAMMOUDI AL-SAADI - Saddam Hussein's top scientific adviser surrenders in Baghdad. Saadi, who acted as liaison to U.N. weapons inspectors, arranged his surrender after learning he was No. 55 on the list. April 13 - WATBAN IBRAHIM HASAN AL-TIKRITI - Saddam's half-brother was turned over to the U.S. military. Saddam removed him as interior minister in 1995...