What we know about the NYC bombing device

— -- The explosive device detonated in the New York City subway system Monday morning did not fully shatter but had the ability to impose more injuries, according to a law enforcement source.

Authorities called the homemade device -- allegedly made by 27-year-old Akayed Ullah -- an "improvised low-tech explosive."

Ullah "had strapped to his body an I.E.D., a pipe bomb that he had made using a metal pipe filled with ... screws held together under his jacket with wires and zip ties," Joon Kim, acting U.S. attorney for the Southern District of New York, said at a news conference today.

The bomb was built from a 12-inch-long pipe, black powder and rigged with a 9-volt battery and a wire that came from a Christmas light, a law enforcement source told ABC News.

“He did follow some of the instructions that you can find readily online, unfortunately, to create such a device,” New York Police Department counterterrorism chief James Waters told ABC News. “A Christmas light bulb is one of those components.”

Ullah allegedly aimed to "murder as many innocent human beings as he could and to blow himself up in the process -- all in support of a vicious terrorist cause," Kim said.

But the pipe failed to fully shatter and a 6-inch piece was discovered completely intact.

“This could have been worse,” the law enforcement source said.

Ullah is charged with five federal counts, including use of a weapon of mass destruction and bombing a place of public use.

The charging document said law enforcement personnel found a 9-volt battery inside Ullah’s pants pocket, wires connected to the battery running under his jacket and fragments of metal pipe. There was also a remnant of what appeared to be a Christmas tree light bulb attached to the wires.

Kim said a search Monday "of his apartment in Brooklyn revealed metal pipes, pieces of wires and metal screws, consistent with the bomb materials recovered at the scene."

The FBI lab in Quantico, Virginia, and the NYPD bomb squad are analyzing components of the explosive.

The Monday morning explosion occurred in an underground passageway near the Port Authority Bus Terminal, sending commuters scrambling to evacuate a major transit hub just blocks from Times Square.

Despite the rush-hour crowds, officials said, only five people suffered minor injuries.

Ullah, originally from Bangladesh, made statements to police indicating he “was inspired by ISIS to carry out” the attack and said, “I did it for the Islamic State,” according to the charging document.

Some of the material he viewed included instructions to attack at home if unable to travel overseas to join ISIS on the battlefield, the document alleges.