New York ( CNN ) -- A confessed terror plotter calmly told a jury how he acquired the ingredients to make the bombs that he and his co-conspirators planned to detonate on New York subway trains during rush hour , killing many . If the attack was against the United States , then it was `` moral , '' Najibullah Zazi said Wednesday during his second day of testimony in federal court in New York . Zazi , the mastermind behind a plot to rig backpacks with explosives and blow them up on trains , is testifying this week against Adis Medunjanin , the only member of the trio on trial . During his testimony , Zazi detailed how he bought the chemicals from beauty shops and other ingredients from Walmart and Lowe 's and then searched for crowded areas to detonate the explosives . Zazi , an immigrant from Pakistan , and Zarein Ahmedzay , an immigrant from Afghanistan , have already pleaded guilty to terror charges . Zazi said the group was trained in Pakistan by al Qaeda in 2008 and 2009 and then returned to the United States with instructions to attack . The group decided to detonate three bombs on a busy subway train during the Muslim holy month of Ramadan , also around the anniversary of the 9/11 attacks , Zazi said . He testified that one of his al Qaeda handlers told them the attack should send a message to incoming President Barack Obama to pull American troops from Afghanistan . But e-mails monitored by authorities may have helped to foil the plot . Prosecutors in court showed several e-mails they say that Zazi sent in which he asks a person in al Qaeda about a formula for a bomb . During cross examination , Robert Gottlieb , Medunjanin 's attorney , tried to show that his client had had a falling out with Zazi before the plot was created . Medunjanin 's trial is expected to last three weeks . Authorities widely regard the plot as the most serious al Qaeda attempt to launch an attack on American soil since 9/11 . CNN 's Kiran Khalid and CNN terrorism analyst Paul Cruickshank contributed to this report .
Confessed subway bomb plotter Najibullah Zazi testifies against alleged co-conspirator . Zazi testifies the group traveled to Pakistan for terrorist training . Adis Medunjanin is the only member of the trio on trial ; the other two pleaded guilty .