What we know about the Boston Marathon bombing and its aftermath

Two days after explosives killed three people and wounded more than 180 during the Boston Marathon, details continue to trickle in as investigators sort through evidence.

WHAT'S NEW

-- Two men seen in images near the finish line of Monday's Boston Marathon, moments before two bombs there exploded, are of "high interest" and are considered "possible suspects," a law enforcement official said. A circular sent out Wednesday by authorities indicated the attached photos, showing the two men, were being sent around "in an attempt to identify the individuals." The official said the men were of interest because of where they were at a particular time and what they were carrying. One of the men is seen carrying a black backpack. The source said that authorities had not yet identified the two men by name and that the photographs were not being released to the public for fear of impeding the investigation.

-- As of Wednesday evening, Boston-area hospitals had released at least 112 of the 178 people treated for injuries sustained in Monday's attack near the Boston Marathon's finish line, according to a CNN tally. Thirteen of those still hospitalized remain in critical condition, hospital officials said.

PREVIOUSLY REPORTED

Source: Bombs were in pressure cookers
Source: Bombs were in pressure cookers

    JUST WATCHED

    Source: Bombs were in pressure cookers

MUST WATCH

Source: Bombs were in pressure cookers 02:28
Student was filming Boston Marathon
Student was filming Boston Marathon

    JUST WATCHED

    Student was filming Boston Marathon

MUST WATCH

Student was filming Boston Marathon 02:52

Investigation

-- Significant progress has been made in the investigation but there has been no arrest, the FBI told CNN.

-- After sources told CNN that an arrest had been made, sources with the Department of Justice and Boston Police Department each said that no arrest had been made.

-- A source with Boston law enforcement said, "We got him," but would not clarify whether that meant an identification had been made or an arrest carried out.

-- Some federal sources said that it would be going too far to say even that an identification had been made, but several sources in Boston disputed that, saying a clear identification had been made.

-- Investigators believe they have identified a suspect in the marathon bombings, a source who has been briefed on the investigation told CNN's John King. The possible breakthrough came from an analysis of video from a Lord and Taylor department store near the site of the second blast, and video from a Boston TV station helped as well, the official said.

-- Obama received updates overnight about the investigation, a White House official said.

-- White House officials have been briefed by senior members of the federal response and law enforcement team over the past two days.

-- Authorities are processing "the most complex crime scene that we have dealt with in the history of our department," said Ed Davis, the Boston police commissioner.

-- Forensic specialists and dogs trained to detect explosive devices and their residue were at the scene of the blasts. A command post has been created, with 1,000 officers conducting interviews and gathering details.

-- Authorities have received 2,000 tips from around the world, said Richard DesLauriers, the special agent in charge of the FBI's Boston office. "Someone knows who did this," he said.

The casualties

Tracking suspects in the Boston bombings
Tracking suspects in the Boston bombings

    JUST WATCHED

    Tracking suspects in the Boston bombings

MUST WATCH

Tracking suspects in the Boston bombings 03:16
Mapping out the marathon terror attack
Mapping out the marathon terror attack

    JUST WATCHED

    Mapping out the marathon terror attack

MUST WATCH

Mapping out the marathon terror attack 03:58
Photographer captured agony of bombings
Photographer captured agony of bombings

    JUST WATCHED

    Photographer captured agony of bombings

MUST WATCH

Photographer captured agony of bombings 02:43
Beware fake Boston bombing charities
Beware fake Boston bombing charities

    JUST WATCHED

    Beware fake Boston bombing charities

MUST WATCH

Beware fake Boston bombing charities 01:32

The blasts left three people dead.

They are:

-- Martin Richard, an 8-year-old boy with a gap-tooth grin and bright eyes. He loved to run and play in his yard.

-- Krystle Campbell, a 29-year-old freckle-faced woman described by her mother as having "a heart of gold."

-- Lingzi Lu, a Boston University graduate student in mathematics and statistics.

She and two friends were watching the race near the finish line when the blasts erupted, BU Today reported. The second student was in stable condition at Boston Medical Center; the third student was not hurt, it said.

The explosions wounded 183 people.

Of them:

-- Martin's mother and sister are among the wounded. His mother underwent surgery for a brain injury, and his 6-year-old sister lost her leg.

-- Doctors say dozens of victims suffered injuries to their legs that involve blood vessels, bone and tissue.

-- The bombings resulted in at least 13 amputations and left doctors picking ball bearings out of victims in the emergency room, a terrorism expert briefed on the investigation said.

The explosions

-- A lid to a pressure cooker, thought to have been used in the bombings, was found on a roof near the scene of the blasts, a federal law enforcement official with knowledge of the investigation tells CNN.

-- The two bombs hit 12 seconds apart near the marathon's finish line.

-- One of the two bombs was housed in a pressure cooker hidden inside a backpack, the FBI said. To maximize the impact of the shrapnel, the device may have included "nails, BBs and ball bearings."

-- The second bomb was also in a metal container, but there's not enough evidence to determine whether it too was in a pressure cooker, the agency said.

-- Evidence recovered from the scene will be sent to the FBI's lab in Quantico, Virginia, where analysts will attempt to reconstruct the devices used in the attack.

Pressure cooker bombs

-- The simplicity of the bomb makes it hard to trace it to any particular group, an official said.

-- The "recipe" for the bombs ignited by pressure cookers can be found widely on the Internet.

-- In 2004, Homeland Security issued an advisory about pressure cooker bombs.

-- They are made by placing TNT or other explosives in a pressure cooker and attaching a blasting cap at the top, the advisory said. Pressure cooker bombs are made with readily available materials.

-- Though it could indicate domestic terrorism, such bombs have been used in a handful of instances related to international terrorism attempts over the last few years, an official said.

Terror group links

-- No connection has been made to any terrorist group or individual.

-- "There is no reporting indicating a foreign connection, or any reaction from al Qaeda," a senior U.S. official said.

-- Obama described the bombings as an act of terrorism, but said it is unclear whether they were the work of a group or "a malevolent individual."

-- The Pakistani Taliban has said it was not involved in the attack.

-- Authorities don't have a sense of what the motive is, and no one is in custody, an official said.

-- DesLauriers, the FBI special agent, asked the public to report anyone who talked about targeting the marathon or showed interest in explosives. He urged anyone who might have heard explosions in remote areas -- possibly by someone testing a bomb -- or seen someone carrying "an unusually heavy, dark-colored bag" around the time of the attack to come forward.

No Saudi connection

-- U.S. officials have said that more than one Saudi has been interviewed, including a 20-year-old student who was questioned as a possible witness.

-- But a U.S. official said the student "was just in the wrong place at the wrong time."

-- The Saudi Embassy in the United States said no Saudi appears to have been involved.

"The embassy stresses that there is no evidence, according to U.S. authorities, of involvement of any Saudi national in the bombings," it said Tuesday in a statement.

-- The investigation is inconclusive.

"They thought they had something with the Saudi national, and that evaporated," a senior law enforcement official said. "There's no sense that they have latched onto anybody or any motive."

-- Authorities are asking those who may have video or pictures taken of the scene around the time of the blasts to call city or FBI hot lines.

Security elsewhere

-- Cities have stepped up security after the attacks, including Washington, New York, Miami, Chicago, Atlanta and Los Angeles.

-- British police said they are reviewing the security plan for the London Marathon scheduled for Sunday. The marathon will observe 30 seconds of silence and is urging runners to wear a black ribbon to mark the Boston tragedy.

Reaction

-- "Boston is not going to be intimidated by this," said Secretary of State Kerry, a former U.S. senator from Massachusetts, in testimony to the House Foreign Affairs Committee Wednesday. "But we are going to find out who did this. The police work being done is extraordinary. The FBI is remarkable. There is a great deal of forensic evidence. We are hopeful we can bring people to justice."

-- "The Islamic Republic condemns killing of innocent people in U.S. Boston, Pakistan, Afghanistan, Iraq and Syria in equal measure," Iran's Ayatollah Ali Khamenei said Wednesday, according to a report from the country's state-run Press TV.

Tributes

-- Obama will travel to Boston on Thursday for an 11 a.m. interfaith service dedicated to the victims.

-- Crowds gathered for a vigil on the Boston Common on Tuesday night. They sang songs and lit candles, and some wept.

-- In New York, the Yankees played "Sweet Caroline" during their game against the Arizona Diamondbacks in a tribute to the victims. The Boston Red Sox team has played the Neil Diamond song during its games for the past 15 years.