What we know about the Boston Marathon bombing and its aftermath

CNN News Service | 4/16/2013, 9:23 a.m.

* The device may have been placed in a trash can, from which shrapnel would have been created when it detonated.

* Authorities searched an apartment late Monday in the town of Revere, northeast of Boston, and removed items, but would not say how the search might be linked to the investigation.

* The official said the Revere search is connected to a young Saudi man on a student visa who has been questioned at a hospital.

* The search found nothing related to the bombing, the official said. It took place with consent, so no search warrant was needed, a federal law enforcement official told CNN.

* U.S. and Saudi officials said more than one Saudi has been interviewed. CNN knows of a male, whose apartment was searched, and a female. All those interviewed are cooperating, and none has been labeled a suspect, Saudi officials, said.

* At least two Saudi nationals were wounded in the Boston Marathon bombings, a Saudi Embassy official told CNN. Neither is a suspect in the attack, the Saudi official said, citing U.S. officials.

* One is a student, 20, who suffered shrapnel wounds and was questioned as a possible witness, the source said.

* The other is a medical student who was at the marathon with her husband and child, the source said.

* Investigators have urged police to be on the lookout for a "darker-skinned or black male" with a possible foreign accent in connection with Monday's bombings, according to a law enforcement advisory obtained by CNN. The man, seen with a black backpack and sweatshirt, was trying to enter a restricted area about five minutes before the first explosion, the notice says.

* The FBI has taken the investigation's lead role, said DesLauriers, the special agent in charge of the bureau's Boston office.

* "The situation remains fluid, and it remains too early to establish the cause and motivation," the FBI's Boston Division said in a statement asking people to call in with any information, images or details related to the explosions.

* The Pakistani Taliban was not involved in the attack, spokesman Ihsanullah Ihsan said.

* Federal law enforcement has been placed on "Level 1 mobilization," U.S. government sources said. "That's equivalent to all hands on deck," one official said. A senior federal official told CNN that teams were on standby to search flights leaving the United States; no team had been activated.

The bombs:
* A knowledgeable source called the bombs "crude."

* The bombs appear to have been inside metal pressure cookers that were in backpacks, a federal law enforcement official with knowledge of the investigation told CNN.

* A law enforcement official said it was "likely, but not certain" that a timing device was used and that at least one of the bombs was not activated by a cell phone.

* In all, 176 people were treated at area hospitals after the blasts, Police Commissioner Davis told reporters. It was not clear if he was including the fatalities.