Detonator ... syringe
In one blog he says: "loneliness leads me to other problems".
Photos of the Abdulmutallab appeared on ABC News in the US.
A six-inch long packet of the high explosive chemical called PETN - weighing about 80 grams - was sewn into the crotch of the underwear.
A government test with 50 grams of PETN blew a hole in the side of an airliner. That was the amount in the bomb carried by the so-called shoe bomber Richard Reid over Christmas 2001.
The underpants bomb would have been one and a half times as powerful.
Abdulmutallab allegedly attempted to detonate the device as the plane came in to land at Detroit airport.
Explosive ... PETN powder
A second picture showed the burnt and melted syringe which would have been used to ignite the device.
Postings
Al-Qaeda admitted last night that it was behind the Christmas Day attempt to blow the American airliner.
Terror chiefs bragged that Abdulmutallab, a London-educated Nigerian, was a "martyrdom-seeking brother" who "reached his target".
They said he failed because "a technical fault occurred leading to a lack of complete explosion".
But they warned of atrocities and called on Islamists to attack Western embassies.
Last night federal intelligence officials were reviewing the internet postings believed to have been written by Abdulmutallab, said the Washington Post.
The newspaper, which has reviewed the postings reported that farouk 1986 (a combination of his middle name and his birth year) searched for friends online through Facebook and in Islamic chat rooms.
In one such posting he wrote: "My name is Umar but you can call me Farouk."
Bomber ... Umar Abdulmutallab
A posting from January 2005, when he was attending boarding school, read: "I have no one to speak to. No one to consult, no one to support me and I feel depressed and lonely. I do not know what to do. And then I think this loneliness leads me to other problems."
Farouk1986 also wrote about considering applications to US and British universities - including University College London from where he graduated in June 2008
In a June 2005 posting, when Mr Abdulmutallab is now known to have been in Yemen, farouk1986 wrote that he was in Yemen for a three-month Arabic course, saying that "it is just great" and raving about about the capital's shopping and restaurants, including Pizza Hut and KFC.
Lonely
As a student at the British boarding school in Togo, Farouk1986 wrote that he was lonely because there were few other Muslims.He said: "I'm active, I socialise with everybody around me, no conflicts, I laugh and joke but not excessively," he wrote in one posting.
In the same posting he also wrote about desire and marriage, saying that at 18 he was not yet ready for it.
"The Prophet advised young men to fast if they can't get married but it has not been helping me much and I seriously don't want to wait for years before I get married," he wrote.
He said he had not started searching for partners because of social norms such as having "a degree, a job, a house, etc. before getting married."
But, he said, "my parents I know could help me financially should I get married, even though I think they are also not going to be in favour of early marriage."
He also wrote of his "dilemma between liberalism and extremism" as a Muslim.
He wrote in 2005: "The Prophet said religion is easy and anyone who tries to overburden themselves will find it hard and will not be able to continue".