rom Lalit K Jha Washington, Jun 23 (PTI) A 29-year-old Morrocan has pleaded guilty of plotting a suicide attack on the US Capitol Building here in February as part of what he believed to be a terrorist operation, the US Justice Department said. Amine El Khalifi, a resident of Alexandria in Virginia, yesterday pleaded guilty before US District Court Judge James Cacheris to one count of attempted use of a weapon of mass destruction against the US Capitol Building, four months after he was charged in an undercover FBI operation. As part of the plea agreement, the US and El Khalifi agree that a sentence within a range of 25 years to 30 years incarceration is the appropriate disposition of this case. Sentencing has been scheduled for September 14, 2012. El Khalifi, an illegal immigrant from Morocco, was arrested and charged by criminal complaint on February 17. His arrest was the culmination of an undercover operation during which he was closely monitored by the FBI Washington Field Office's Joint Terrorism Task Force (JTTF). The explosives and firearm that he allegedly sought and attempted to use had been rendered inoperable by law enforcement and posed no threat to the public. "El Khalifi sought to bring down the US Capitol and kill as many people as possible," said US Attorney Neil MacBride. "He admitted today that he picked the targets, weapons, and means of the suicide attack while working with someone he believed was an al-Qaeda operative," he said in a statement. "El-Khalifi admitted that he attempted to carry out a suicide attack on the US Capitol as part of what he believed would be a terrorist operation," said Assistant Attorney General Lisa Monaco.