Chechen-origin teenager Dzhokhar Tsarnaev apparently used his cell phone to blow up the pressure cooker bomb at the Boston Marathon last week that killed three people and wounded nearly 200 others, according to a criminal complaint filed by the Federal Bureau of Investigation in an American court.
In the complaint, the FBI alleges that the suspect appeared calm while there was chaos all around after the blasts at the finish line of the marathon on April 15.
The FBI filed the complaint against 19-year-old Dzhokhar, as he was produced before a district court which temporarily was his hospital room where he is being treated of injuries.
The court fixed May 30 for Dzhokhar's first hearing in the Massachusetts district court.
Dzhokhar is charged with conspiring to use "weapon of mass destruction" and faces the death penalty if convicted.
In the 10-page complaint, FBI special agent Daniel Geneck gives the sequence of events and the information to sufficiently establish the requisite probable cause. "It does not include each and every fact known to me," he said.
Based on the information obtained from the security cameras, Geneck said the two suspects -- Tamerlan Tsarnaev, 26, and Dzhokhar Tsarnaev -- were first spotted near the bombing site 11 minute before the first bomb explosion.
While Tamerlan was wearing a dark-coloured baseball cap, sunglasses, a white shirt, dark coat and tan pants, his brother was wearing a white baseball cap backwards, a gray hooded sweatshirt, a lightweight black jacket, and dark pants.
Thereafter, the two were seen moving towards the marathon finish line, which was occupied by thousands of people, which is reflected through various security cameras.
At some point Dzhokhar appears to look at his phone, which is held at approximately waist level, and may be manipulating the phone, Geneck said.
"Approximately 30 seconds before the first explosion, he lifts his phone to his ear as if he is speaking on his cell phone, and keeps it there for approximately 18 seconds. A few seconds after he finishes the call, the large crowd of people around him can be seen reacting to the first explosion," the complaint said.
"Virtually every head turns to the east (towards the finish line) and stares in that direction in apparent bewilderment and alarm," Geneck said, adding that Dzhokhar, virtually alone among the individuals in front of the restaurant, appears calm.
According to the video footage, the two brothers are seen standing about half a block from the restaurant where the bombing appeared.
In another footage, they are seen standing about half a block from the restaurant where the bombing appeared.
Approximately seven minutes before the first explosion, Tamerlan can be seen detaching himself from the crowd and walking east towards the marathon finish line.
Fifteen seconds later, he can be seen passing directly in front of the Forum restaurant and continuing in the direction of the location where the first blast occurred.
His knapsack is still on his back, the FBI agent said.
Around 2:45 pm, Dzhokhar can be seen detaching himself from the crowd and walking east toward the finishing line. He appears to have the thumb of his right hand hooked under the strap of his knapsack and a cell phone in his left hand.
"Approximately 15 seconds later, he can be seen stopping directly in front of the Forum restaurant and standing near the metal barrier among numerous spectators, with his back to the camera, facing the runners. He then can be seen apparently slipping his knapsack onto the ground," the FBI agent said, adding that a photograph taken from the opposite side of the street shows the knapsack on the ground at Dzhokhar's feet.
The Forum restaurant video shows that Dzhokhar remained in the same spot for approximately four minutes, occasionally looking at his cell phone and once appearing to take a picture with it.
"Thirty seconds before the first explosion, he lifts his phone to his ear as if he is speaking on his cell phone, and keeps it there for approximately 18 seconds. A few seconds after he finishes the call, the large crowd of people around him can be seen reacting to the first explosion," he said.
"He glances to the east and then calmly but rapidly begins moving to the west, away from the direction of the finish line. He walks away without his knapsack, having left it on the ground where he had been standing. Approximately 10 seconds later, an explosion occurs in the location where Bomber Two had placed his knapsack," the FBI agent said.
It was only three days later on April 18 that the FBI published video and photographic images of the two suspect on its web site. Those images were widely rebroadcast by media outlets all over the country and the world.
It was near midnight on April 18, 2013, they received information that an individual carjacked a vehicle at gunpoint in Cambridge, Massachusetts.
A victim of the carjacking told law enforcement officials that while he was sitting in his car on a road in Cambridge, a man approached and tapped on his passenger-side window.
When the victim rolled down the window, the man reached in, opened the door, and entered the victim's vehicle. The man pointed a firearm at the victim and stated, "Did you hear about the Boston explosion?" and "I did that."
The man with the gun forced the victim to drive to another location, where they picked up a second man. The two men put something in the trunk of the victim's vehicle.
The gunman took the victim's keys and sat in the driver's seat, while the victim moved to the front seat. The second man entered the vehicle and sat in the rear seat.
"The man with the gun and the second man spoke to each other in a foreign language," the FBI agent said.
And while they were driving, the gunman demanded money from the victim, who gave him USD 45, the complaint said.
"One of the men compelled the victim to hand over his ATM card and password. They then drove to an ATM machine and attempted to withdraw money from the victim's account. The two men and the victim then drove to a gas station/convenience store in the vicinity of 816 Memorial Drive, Cambridge. The two men got out of the car, at which point the victim managed to escape," it said.
A short time later, the stolen vehicle was located by law enforcement in Watertown. As the men drove down, they threw at least two small explosive devices out of the car.
"A gun fight ensued between the car's occupants and law enforcement officers in which numerous shots were fired. One of the men was severely injured and remained at the scene; the other managed to escape in the car. That car was later found abandoned a short distance away, and an intact low-grade explosive device was discovered inside it.
"In addition, from the scene of the shootout on Laurel Street in Watertown, the FBI has recovered two unexploded IEDs, as well as the remnants of numerous exploded IEDs," Geneck said, adding that these two men were Tamerlan and Dzhokhar.
While Tamerlan was a lawful permanent resident, Dzhokhar entered the US in April 2002, and is a naturalised US citizen.
According to the complaint, a preliminary examination of the remains of the explosive devices that were used at the marathon revealed that they were low-grade explosives that were housed in pressure cookers of the same brand.
"The cookers also contained metallic BBs and nails. Many of the BBs were contained within an adhesive material. The explosives contained green-coloured hobby fuse," it said.
"A preliminary examination of the explosive devices that were discovered at the scene of the shootout in Watertown and in the abandoned vehicle has revealed similarities to the explosives used at the Boston marathon," the complaint said.
"The remnants of at least one of the exploded IEDs at the scene of the shootout indicate that a low-grade explosive had been contained in a pressure cooker. he explosive also contained metallic BBs contained within an adhesive material as well as green-coloured hobby fuse.
“The intact low-grade explosive device found in the abandoned car was in a plastic container and wrapped with green-coloured hobby fuse," Geneck alleged.
Dzhokhar was arrested on April 19. A University of Massachusetts at Dartmouth identification card, credit cards, and other forms of identification were found in his pockets. All of them identified him as Dzhokhar.
"The FBI seized from his room, among other things, a large pyrotechnic, a black jacket and a white hat of the same general appearance as those worn by Bomber Two at the Boston marathon on April 15, 2013, and BBs," he said.