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San Bernardino shooting: Timeline of how the rampage unfolded

Here's how the events, which span three active crime scenes, unfolded according to San Bernardino police, who are trying to determine a motive.

The chaos in San Bernardino, California, on Wednesday began at a social services center and ended several hours later in a police firefight that left two suspected shooters dead.

By the end of the carnage, investigators tallied 14 victims and 21 wounded — considered the worst mass shooting in modern U.S. history since Newtown, Connecticut, in December 2012.

Here's how the events, which span three active crime scenes, unfolded according to San Bernardino police, who are trying to determine a motive:

Wednesday 11 a.m. PT

Initial 911 calls report shots fired at the Inland Regional Center, a state-run facility that serves people with developmental disabilities. Police say the shooting took place during a holiday party and lasted only a few minutes before the suspects fled. They had fired some 75 rifle rounds.

One of the suspects — later identified as county health inspector Syed Rizwan Farook, 28 — had attended the party that morning, according to reports, but reportedly left after a dispute. Police believe between 10 and 30 minutes went by between Farook's departure and the suspect's return to the conference room.

11:07 a.m.

Firefighters begin arriving at the scene within seven minutes of the first 911 calls.

11:20 a.m.

Julie Paez, an inspector with the county's Department of Health attending the holiday party, sends a text to her family, the Los Angeles Times reported: "Love you guys. Was shot," it read. Paez survived two gunshot wounds and a broken pelvis.

11:40 a.m.

Police begin reporting multiple victims shot at the scene. Several roads are shut down in the area.

12:25 p.m.

Police say they are looking for as many as three shooters after sweeping the building and determining the suspects fled. Emergency responders are also seen treating people outside and ambulances rush in and out to take the injured to the hospital.

12:30 p.m.

President Obama is briefed on the shooting by Homeland Security. "It does appear that there are going to be some casualties, and obviously our hearts go out to the victims and the families," he later tells CBS News.

1:05 p.m.

Police confirm at least three people were killed. Reports come out from family members of survivors who say the shooters were wearing "military-style" attire.

2 p.m.

Police confirm at a news conference that there are 14 dead and 17 wounded. Area buildings are on lockdown as authorities search for the suspects.

2:30 p.m.

San Bernardino Police Chief Jarrod Burguan declines to say what kind of weapons were used, but that the shooters "were on a mission" and "came in with a purpose."

3:05 p.m.

Reports come in of police in pursuit of a black SUV that had fled the scene. A shootout with police ensues a few miles away.

3:20 p.m.

Police aim guns at a dark-colored SUV with shattered windows on a residential street. A firefight ensues. Nearly two dozen officers fired some 380 rounds at the suspects. The suspects return fire with 76 rounds. Local media reports say a person appears to be on the ground, but it is unclear who they are or what their injuries may be.

3:30 p.m.

Police confirm shots have been fired and a suspect is down near the SUV. According to reports, a male suspect's body is on the street, while a female suspect's body has been pulled from the car. Some 1,600 unused rounds are found on the two suspects, police would later say.

San Bernardino police Sgt. Vicki Cervantes said one officer suffered non-life-threatening injuries during the shootout.

5:05 p.m.

Police serve a search warrant on a home in Redlands in connection with the shooting. An Associated Press reporter watched as a half-dozen vehicles carrying helmeted police drove into the area. One officer carrying an assault rifle ordered reporters to clear the area, and an armored vehicle parked outside a row of homes.

5:50 p.m.

Police say a person was detained who was seen running near the gunbattle, but it was not clear if that person is connected to the shooting.

7:40 p.m.

A law enforcement official has identified Farook as one of the suspects in a mass shooting in Southern California. Police also confirm that the two suspects — Farook and a woman — were killed in the gunbattle.

8:55 p.m.

The brother-in-law of Farook says at a news conference that he was stunned to hear of his relative's alleged involvement in the shooting. Farhan Khan, who is married to the sister of Farook, spoke to reporters at the Anaheim office of the Council on American-Islamic Relations.

Khan says he last spoke to Farook about a week ago. He added that he had "absolutely no idea why he would do this. I am shocked myself."

10:10 p.m.

Police say they believe the man and woman killed in the gunbattle were the only two shooters. Burguan identifies the woman killed as 27-year-old Tashfeen Malik, who is described as Farook's wife.

The couple had been living in Redlands with Farook's mother.

No motive is known, but terrorism has not been ruled out.

Thursday 7:35 a.m. PT

Loma Linda University Medical Center CEO Kerry Heinrich says of the five patients being treated at its facility, two remain in critical condition and three are in stable condition.

8:10 a.m.

Obama says the FBI is leading the investigation, and that it's still unclear whether the shooting was either terrorism-related or workplace-related.

He adds that legislators and all Americans have a part to play to make sure that "when individuals want to do harm, we make it a little harder for them to do it."

9:30 a.m.

Law enforcement officials tell NBC News that the SUV in which Farook and Malik made their getaway, and in which they were killed in a gunbattle with police, was a rental with Utah plates.

Officials say Farook rented it "recently," which they believe was another step in preparation for the attack.

9:45 a.m.

Police at a news conference say the suspects fired as many as 75 rounds at the Inland Regional Center, and then another 76 rounds during the pursuit with police. A remote-controlled car with three pipe bombs was also found at the social services center but it did not detonate, Burguan says.

Officials add that a second officer was wounded during the police shootout. The overall number of wounded rises to 21 from 17.

The search of the Redlands home, where the couple's name was on the lease, also turns up an additional 12 pipe bomb devices and thousands of rounds of ammo, police say. "Clearly they were equipped" to launch another attack if they wanted to, Burguan adds.

The FBI confirms that Farook had rented the SUV — a black Ford Expedition — about three or four days ago, and it was supposed to be returned on the day of the rampage.

10:15 a.m.

Farook appears to have been radicalized, authorities tell NBC News. The extent of his radicalization wasn't immediately clear, but he had been in touch with persons of interest in the Los Angeles area who have expressed jihadist-oriented views.

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