LOS ANGELES (CNS) – The married couple who carried out the mass shooting at a San Bernardino care facility took part in target practice at Southland shooting ranges, including once just days before the terrorist attack, federal officials said today.

Investigators also confirmed that a former neighbor of Syed Farook purchased the assault rifles that were used in the shooting, and they were trying to determine how the weapons wound up in the hands of Farook and his wife, Tashfeen Malik.

David Bowdich, assistant director in charge of the FBI’s Los Angeles field office, said investigators have conducted more than 400 interviews and collected about 320 pieces of evidence as they work to paint a picture of how the couple planned and carried out the attack, and they want to track down anyone who may have participated in the planning or profited from it.

“And I’m not saying there is anything like that, but we will leave no stone unturned,” he said.

Bowdich said Farook, 28, and Malik, 27, had been “radicalized” for some time, but it was still unclear how and by whom. But they were clearly prepared to carry out Wednesday’s shooting at the Inland Regional Center that killed 14 and injured 21 — the deadliest terror strike on American soil since 9/11.

“Yes, we do have evidence that both of these subjects participated in target practice (at) some ranges” in the Los Angeles metropolitan area, including once “within days of this event,” Bowdich said.

He said investigators are working with their “foreign counterparts” as they look into the background of the couple.

“We are attempting to expand that investigation out and build it and build a picture of each person, the timeline and ultimately the crimes that they committed,” he said.

On Saturday, FBI agents with a search warrant raided the Riverside home of Enrique Marquez, a former neighbor of Farook.

Federal agents entered the Tomlinson Avenue home just after 1 a.m., Federal Bureau of Investigation spokeswoman Laura Eimiller said. Eimiller declined to comment on the reason for the raid at the residence, reported to be next door to where Farook once lived.

John D’Angelo, assistant special agent in charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives in Los Angeles, confirmed that Marquez purchased the two assault rifles that were used in the attack.

“Right now our major concern … is determining how those firearms … got from Marquez to Farook and Malik,” he said.

He said other firearms found by investigators after the attack had been legally purchased by Farook between 2007 and 2012 from federally licensed dealers.

The Joint Terrorism Task Force has now taken the lead in the investigation into the shooting at the Inland Regional Center. President Barack Obama said Sunday night that the attack had been “an act of terrorism designed to kill innocent people.”

Farook and Malik had been married two years and had a 6-month-old daughter. Intelligence sources said Malik posted a statement of allegiance to ISIS leader Abu Bakr al-Baghdadi  just before the killing began, and an ISIS online radio broadcast said Farook and Malik were ISIS supporters.

“Two followers of Islamic State attacked several days ago a center in San Bernardino,” media reports quoted the ISIS broadcast as saying. ISIS did not directly take responsibility for the attack, but praised Farook and Malik as “martyrs.”

The couple was killed in a gunbattle with police about seven hours after the initial shooting at the Inland Regional Center, which provides treatment for people with developmental disabilities. Investigators found evidence Farook and Malik destroyed their mobile phones the day before the shootings.

Family members have said they had not seen any evidence the U.S.-born Farook, nor his Pakistani wife, had been “radicalized.” American investigators are looking into whether Malik radicalized Farook.

In a nationally broadcast speech Sunday night, Obama sought to reassure the nation, insisting “we will prevail.”

The victims who died Wednesday were Sierra Clayborn of Moreno Valley, 27; Aurora Godoy of San Jacinto, 26; Damian Meins of Riverside, 58; Robert Adams of Yucaipa, 40; Isaac Amanios of Fontana, 60; Bennetta Bet-Badal of Rialto, 46; Harry Bowman of Upland, 46; Juan Espinoza of Highland, 50; Shannon Johnson of Los Angeles, 45; Larry Kaufman of Rialto, 42; Tin Nguyen of Santa Ana, 31; Nicholas Thalasinos of Colton, 52; Yvette Velasco of Fontana, 27; and Michael Wetzel of Lake Arrowhead, 37.

On Wednesday morning, Farook left the couple’s infant daughter with his mother, claiming he was taking his wife to a doctor’s visit and didn’t want to bring the baby along, according to Hussam Ayloush, the executive director of the Council on American-Islamic Relations-Los Angeles (CAIR-LA).

Farook was a five-year employee of the San Bernardino County public health agency, which was holding a holiday party when the shooting erupted.

The Los Angeles Times reported that Farook traveled to Saudi Arabia last year and spent nine days there before returning with a new wife he met online, Malik, who was originally from Pakistan. The Pakistani government said over the weekend it is investigating local aspects of the attack.

The Times and other media outlets, citing a senior government official who spoke on condition of anonymity, have reported that Farook was in contact with a number of extremists and at least one person being monitored by federal officials, a Pakistani named Roshan Zamir Abbassi, who is an assistant Imam in San Bernardino, where Farook worshipped. But Abassi told The Times he barely knew Farook and only exchanged occasional hellos and goodbyes.

Meanwhile, most San Bernardino County offices re-opened for business today for the first time since the shooting. However, environmental health employees, the targets of the rampage, will remain off for another week.

Officials also said employees would benefit from added security and access to counseling.