US authorities are searching for at least one person seen in surveillance image near the bomb site. Meanwhile, President Obama has traveled to Boston to attend an interfaith prayer service in memory of the victims.
Federal and local authorities were conducting a massive search Thursday morning in what could be a turning point in the Boston Marathon bombing case.
The new lead reportedly had come to investigators’ attention within the last 24 hours after a person was spotted leaving a dark bag - thought to be black - near one of the explosion sites.
The name of the suspect remained unknown on Thursday morning.
The "Los Angeles Times" and news broadcaster CNN reported that authorities were searching for two suspects.
Investigators have been unable to tell the public the motive behind the two explosions on Monday, which ripped through a central street in Boston lined with crowds of people cheering on marathon runners as they approached the finish line.
"They are making progress. But it's going to take time," Massachusetts Governor Deval Patrick said on CNN. "Every hour, we're closer."
Monday's attack claimed three lives and injured over 170, many of whom required amputation surgery. Based on evidence found at the crime scene, as well as shrapnel recovered from hospital patients, experts believe that the bomb maker filled at least two pressure cookers with black powder, nails and ball bearings with the intention of causing carnage.
Boston tries to heal
An interfaith service at the Roman Catholic cathedral in Boston took place on Thursday morning.
US President Barack Obama and his wife, Michelle, were attending the event. Mitt Romney, who served as Massachusetts governor from 2003 and 2007, also attended the event.
The city continues to look for answers as more information about the victims is released.
On Wednesday, officials confirmed that the third victim was 23-year-old Lu Lingzi. The Chinese national had been enrolled as a graduate student at Boston University.
The blasts also claimed the lives of eight-year-old, Martin Richard, and Krystle Campell, 29, a restaurant manager from the US state.
Local hospitals continued on Thursday to treat at least 10 patients in critical condition.
kms/rc (AP, AFP, Reuters, dpa)