The suspects who allegedly killed 14 people and wounded 21 more during a mass shooting in San Bernardino, Calif., on Wednesday had a dozen explosive devices in their home, police said.

San Bernardino police chief Jarrod Burguan said at a Thursday news conference that “12 pipe bomb-type devices” were found at the home of the two deceased suspects, along with “hundreds of tools” that the two could have used to manufacture other explosive devices. That’s in addition to an unexploded pipe bomb that Burguan said police discovered at the scene of the shooting.

One day after the violent attack, the nation’s deadliest mass shooting since the Sandy Hook Elementary School massacre in 2012, authorities were still working to piece together the precise set of circumstances that surrounded the carnage. But there were some details that emerged.

Burguan said the suspects, who police have identified as Syed Rizwan Farook and Tashfeen Malik, allegedly sprayed between 65 and 75 bullets during a rampage at the Inland Regional Center before fleeing in a dark-colored SUV. They were later killed in a shootout with police.

The chief said police also discovered at least 4,500 additional rounds of ammunition at the home of the married couple, fueling speculation about what the suspects might have been planning. Police had not released an exact motive as of Thursday afternoon, though CNN quoted Burguan as saying that the two “were equipped … and they could have done another attack.”

According to numerous published reports, Farook was an employee of the San Bernardino County Public Health Department, which was hosting a holiday party at Inland Regional Center at the time of the shooting. Burguan is quoted in several reports as saying that Farook left the event angrily and abruptly, then he and his wife returned in tactical gear and began shooting.

Speaking from the Oval Office, President Barack Obama told reporters that the attackers might have had “mixed motives.” The Los Angeles Times quoted a federal law enforcement source as saying that a “combination of terrorism and workplace” was what investigators were focusing on, and they were trying to determine if the act was inspired by or directed by a terrorist group.

Multiple media organizations report that Farook was Muslim, though it’s not clear if he had been radicalized or had any links to religious extremist groups. Co-workers told The Los Angeles Times that he seldom discussed his religion at work, and had attended the same holiday event last year.

A relative told the New York Times the suspects met on an Internet dating site. Farook was born to Pakistani parents in Illinois and Malik was a Pakistani native living in Saudi Arabia. A relative told the newspaper that Farook flew to Saudi Arabia twice, including once to marry Malik. They had been married for about two years, according to an NPR report.

Citing family members, CNN reported that the suspects had a six-month-old daughter that they left at a grandmother’s house sometime on Wednesday. They claimed to be going to the doctor. Instead, police say they went to the party at about 11 a.m. and opened fire. Police believe they were the only two gunmen, and earlier reports of a potential third shooter were inaccurate.

Residents of the Redlands, California, neighborhood where the suspects lived spoke to the BBC and described it “peaceful” and home to “a bunch of innocent people.” The neighbors said there was no indication that the suspects were planning or capable of committing such a shooting.

It was the deadliest mass shooting in the United States since a gunman killed 20 children and six teachers at Sandy Hook Elementary School in December 2012.