"He was someone I would call his right arm," said Major Stan Murphy, the head of intelligence for the US 4th Infantry Division's First Brigade in Tikrit, describing the man who led to the former Iraqi leader's capture at a hideout near there on 13 December.
Murphy said the informant was in detention, ruling out the possibility that he would receive any of the $25 million bounty that the United States had placed on Saddam's head.
"He is a bad man and should rot in jail," the major said.
The man, whose name the military will not reveal, is said to be a long-time aide of Saddam and hailed from one of five major tribes in a 20km stretch around Tikrit, Saddam's hometown.
In addition to helping the fallen dictator elude the Americans for about eight months, the aide - along with four or five other Iraqis - formed the inner circle that helped hide Saddam, implement his orders to the resistance for attacks, finance the insurgency and provide combatants with weaponry, claimed Murphy.
"He (Saddam) would give general guidance … His enablers would then go out to their different tiers below them, give a little more specific guidance, maybe some money or weapons or something, and that tier would go out to the other tiers all the way down to the trigger puller," Murphy said.
But while the other aides shared the burden of labour and their functions overlapped, the man who eventually informed on Saddam was the fugitive strongman's most trusted confidante.
The middle-aged man, whose name or job in the old regime Murphy refused to disclose, had started to serve Saddam in his late-teens or early twenties and had risen to become one of Saddam's most valued sidekicks.
He fits a stock profile of many of the men who served under Saddam. He was balding and heavily overweight, with an almost 130cm (50-inch) waistline, and "loved women", Murphy said.
US soldiers from the 4th Infantry
Division led the hunt for Saddam
He also participated in the old regime's crimes against the Iraqi people, Murphy said, without disclosing the exact nature of his involvement in Saddam's abuses.
Generally, Saddam travelled with a small group of aides who drove and cooked for him that came from a pool of about 20-25 people who hailed from the five families based around Tikrit, Murphy said. He also probably travelled in the common orange and white Passat Toyota taxis.
But Saddam's top enablers did not travel with him and it is not even sure how often they met, with some of their exchanges coming through messengers.
However, although he had been considered important since July, the Americans did not realise how crucial the lieutenant was until the end of November when information about his involvement in resistance activities emerged.
The aide, along with all but one of Saddam's four or five most trusted aides, did not even appear on the US government's blacklist of the top 200 most wanted from Saddam's ousted regime. All but one of them is now in jail.
After escaping three raids in the first week of December, he was captured in Baghdad on 12 December, Murphy said. Under interrogation, he confessed Saddam was hiding at one of two locations in al-Dawr, a farming village near Tikrit.
As US special forces searched the palm groves around two farms, Saddam's most-trusted aide pointed to the secret underground room where the former Iraqi president was hiding, Murphy said.