Thousands of police officers with rifles and armored vehicles patrolled the streets of greater Boston on Friday in the hunt for Dzhokhar Tsarnaev, a 19-year-old college student wanted in connection with the Boston Marathon bombings. He appeared in photos produced by police wearing a white baseball hat.

Residents of the greater Boston area were told to stay at home with their doors and windows closed Friday. Public transport was halted and schools, universities and many businesses were closed as police searched for Tsarnaev. His elder brother, 26-year-old Tamerlan Tsarnaev, was killed in a shootout with police on Thursday night.

At a news conference at 6 p.m. local time on Friday evening, Massachusetts Governor Deval Patrick announced that although Tsarnaev had not yet been apprehended, the stay-in-place order for Boston had been lifted and mass transit reopened. Patrick asked people to remain vigilant.

Massachusetts State Police Colonel Timothy Alben warned Tsarnaev was a "dangerous" individual who was armed, and called on him to give himself up. Twenty streets were searched in the Watertown district of Boston where Tsarnaev was last seen after abandoning the car on Thursday night.

Two brothers

Local authorities had engaged in an armed pursuit of the two men allegedly linked to two deadly explosions at the city's annual marathon which left three people dead and over 170 other people injured.

The brothers were reported to have tried to rob a convenience store close to the prestigious Massachusetts Institute of Technology (MIT) in Cambridge late on Thursday before going on to the university itself.

There, they were engaged in a shootout in which a campus police officer was fatally shot. The brothers then took a car to the Watertown district of the city.

A chase ensued, with the pair reported to have thrown explosives out of the car. Elder brother Tamerlan was killed in the resulting shootout. Dzhokar was able to flee the scene.

Police sealed off the area with some 9,000 officers armed with shotguns, assault rifles and other weapons.

The suspects were identified by both police and a family member as brothers Dzhokhar and Tamerlan Tsarnaev. An uncle of the two told the TV network CNN that the family was ethnically Chechen and Muslim and that the pair had been raised in Kyrgyzstan before moving to the US in 2003.

Tribute to victims

Boston held an emotional tribute on Thursday to the three who died in the bombings on Monday - eight-year-old Martin Richard, Krystle Campbell, of nearby Medford and Chinese graduate student Lu Lingzi.

rc, jm/jr (AFP, AP, dpa, Reuters)