BOSTON -- The City of Boston remains on lockdown as police continue to search nearby Watertown, Mass., where it's believed the second of two suspects wanted in the Boston Marathon bombings may be hiding out. The massive manhunt comes after the first suspect, identified by the Associated Press as Tamerlan Tsarnaev, 26, was killed by authorities earlier Friday following a violent car chase. His brother, identified by the AP as Dzhokhar A. Tsarnaev, 19, remains at large. Federal authorities say he is armed and dangerous.
Massachusetts State Police have called off a search for a green Honda Civic that has been linked to the suspects. Authorities initially said the at-large suspect may have been driving the 1999 Civic, but police said later that the car is in their possession and they are no longer looking for it.
During a noon press briefing, Boston authorities urged Watertown residents there to remain indoors and patient as they continue to follow possible leads.
The Massachusetts State Police Department says officers plan to conduct a controlled explosion at a Cambridge address this afternoon before searching the premises. Further details were not discussed.
Speaking to reporters in Maryland Friday morning, the suspects' uncle urged his 19-year-old nephew to turn himself in and "ask for forgiveness."
Boston Police Commissioner Edward Davis said the latest chapter in the marathon bombings began Thursday night when authorities responded to shots fired on the MIT campus. Upon their arrival, they found MIT campus police officer Sean Collier, 26, shot dead inside his car.
The two men, later identified as the bombing suspects, then carjacked a Mercedes SUV and were pursued by police into Watertown. During the chase, the suspects fired weapons and threw explosive devices at responding officers, who then returned fire, killing one of the suspects. A Boston transit officer was also injured in the exchange of fire.
The second suspect's description, consistent with the description of one released in the Marathon bombing and shows him wearing a white cap, was taken around the time of the attack.
Surveillance video from a 7-Eleven convenience store in Cambridge Thursday night reportedly shows the 19-year-old suspect wearing a gray hooded sweatshirt.
Massachusetts State Police say the brothers were driving in a Honda Civic when they carjacked the Mercedes SUV. They say, for a while, each drove one of the two vehicles, but then abandoned the Honda and reunited in the Mercedes.
The Associated Press reports that the brothers are from a Russian area near Chechnya. They are reported to be permanent U.S. residents who have been in the U.S. for as many as 10 years.
"We believe these are the same individuals that were responsible for the bombing on Monday at the Boston Marathon," Davis said.
The entire Boston pubic transit system as well as public schools and universities in the city are closed. The FAA has also closed airspace above the area of Watertown; Logan Airport remains open.
According to the FBI, Tamerlan Tsarnaev, who they initially labeled "Suspect 1", is seen in surveillance photos wearing a dark hat, dark coat and carrying a backpack. Dzhokhar A. Tsarnaev, who was initially labeled "Suspect 2," is seen wearing a backwards white hat and a dark coat. According to FBI officials, Dzhokhar was the only man seen planting a device at the bombing site.
"It was shortly before the bomb blast went off, within minutes," said Richard DesLauriers, the FBI Special Agent in Charge of the case.
Federal officials said the images show the brothers walking together on Boylston Street through the marathon crowd toward the finish line.
Anyone with tips on the case should call 1-800-CALL-FBI (1-800-225-5324)