The U.S. Federal Bureau of Investigation says authorities believe both suspects in last week's mass shooting in San Bernardino, California were radicalized "for some time," and that there is evidence they pre-planned the deadly attack.
David Bowdich, the FBI's assistant director in charge of the Los Angeles field office, told reporters Monday that the suspected shooters, U.S.-born Syed Rizwan Farook and his Pakistani wife Tashfeen Malik, participated in target practice within days of the attack. He said the FBI is still investigating how long the couple was planning the attack. But he added there is no evidence at this point that the shooters were part of a broader, overseas plot.
Bowdich said investigators are trying to determine how, when and by whom the shooters were radicalized. He said it is possible the radicalization happened through the Internet, and not through any in-person connection.
Earlier Monday, thousands of government workers in San Bernardino started to go back to work.
Farook and Malik carried out the mass shooting at a gathering of local government workers last Wednesday killing 14 people and wounding 21 others. Their car was later spotted and they were killed as they exchanged gunfire with police.
Local officials said there would be increased security in the area that is still coming to terms with what President Barack Obama called an "act of terrorism designed to kill innocent people."
In a rare televised address from the Oval Office late Sunday, President Obama discussed the attack and sought to reassure Americans on the U.S. strategy to combat terror. The president said the two killers had embraced "a perverted interpretation of Islam."
Federal officials said Malik pledged allegiance to an IS militant leader in a Facebook post and that Farook had contact with individuals linked to terror groups.
Obama said the United States has hardened its defenses against terrorist threats. He noted intelligence and law enforcement agencies have disrupted countless plots, both at home and overseas. He said the U.S. military and counterterrorism professionals have relentlessly pursued terrorist networks overseas, disrupting safe havens in several different countries.
But he noted that over the past few years, terrorists are turning to what he called "less complicated acts of violence" like the mass shootings that he said are "all too common in our society," including the San Bernardino attack as one example.
Although the president said his administration is constantly examining its counter-terrorism strategy to see if additional steps are needed to protect Americans, his speech included no new policy changes or announcements.
Instead, he sought to reassure the American public that he and his administration are taking the threat of terrorism seriously.
The president said Congress should act to make sure no one on the U.S. no-fly list is able to buy a gun. He again reiterated his call for lawmakers to tighten U.S. gun laws, saying no matter how effective law enforcement and intelligence are, they cannot identify every would-be shooter. He called it a matter of national security to prevent potential killers from getting guns.
Earlier, Senate Majority Leader Mitch McConnell called on the president to outline plans for a ground force to dismantle the Islamic State terror group.
But Obama told his audience the United States will not be pulled into a protracted ground war in Syria or Iraq, even as it steps up the fight against Islamic State.
"We should not be drawn once more into a long and costly ground war in Iraq and Syria. That is what groups like ISIL want," Obama said.
Finally, the president implored Americans not to turn against Muslims at home, saying IS is driven by a desire to spark a war between the West and Islam. He also called for Muslims to take up the cause of fighting extremism.
VOA White House Correspondent Mary Alice Salinas and Chris Hannas contributed to this report