Story highlights

NEW: Mourners flock to makeshift memorials, leaving flags to show their support

Four Marines and a sailor were killed by Mohammad Youssuf Abdulazeez

Several states are boosting security at recruitment centers

Chattanooga, Tennessee CNN  — 

Paula Proxmire clutched a baseball glove, a baseball and an American flag as she wove through the crowd.

She cried as she left the items just steps away from the spot where a gunman began a shooting rampage last week, killing four Marines and her son – U.S. Navy Petty Officer 2nd Class Randall Smith.

The grassy area beside a strip mall parking lot has become a makeshift memorial filled with American flags, red, white and blue balloons and signs of support. A poster has pictures of the victims beneath a simple description in large black letters: “OUR HEROES.”

As Proxmire visited the site Sunday, a police motorcade drove by, escorting a white hearse with her son’s casket inside. Tears streamed down the grieving mother’s face.

Families and friends of the victims mourned their deaths as authorities continued their investigation into last week’s shootings at two Chattanooga military centers.

At Chattanooga’s East Ridge United Methodist Church, the five victims’ faces flashed across a large screen as congregants lit candles in their memories.

And a large caravan of motorcycles roared between the shooting sites, revving their engines to show support for the victims.

Looking for a motive

Investigators are still digging into the past of gunman Mohammad Youssuf Abdulazeez, described by those who knew him as a devout Muslim, an accomplished student and a well liked peer.

Authorities in the United States and abroad are working to figure out what might have motivated the 24-year-old to shoot up a recruiting center at the strip mall, then drive to a Navy operations support center about 7 miles away and stage another attack. He died in a gunfight with law enforcement.

U.S. Attorney Bill Killian said the shootings are being investigated as an “act of domestic terrorism,” but he noted the incident has not yet been classified as terrorism.

There is nothing connecting the attacker to ISIS or other international terror groups, said Ed Reinhold, special agent in charge of the regional FBI office. And Abdulazeez was not on any U.S. databases of suspected terrorists.

Several new details have emerged in the investigation over the weekend:

• Some of Abdulazeez’s family and friends have told investigators that they detected some changes in his behavior since he returned to the United States from a trip to Jordan last year, a law enforcement official said. But several of his friends also told investigators that they didn’t see any behavior that indicated he would launch an attack.

• Jordanian security investigators have interviewed Abdulazeez’s extended family, asking them where he went and whom he spoke with on his trip, government sources there told CNN.

• As one piece of the puzzle in their investigation of his motive, authorities are looking at a text message from Abdulazeez to a friend before the attack, law enforcement sources told CNN. The message said: “Whoever shows enmity to a friend of Mine, then I have declared war against him.”

• The gunman’s family issued a statement expressing their condolences and saying he suffered from depression. “It grieves us beyond belief to know that his pain found its expression in this heinous act of violence,” the statement read. “We extend our deepest sympathies and condolences to the families of the honorable service members and police officers who were victims of the shooting our son committed on Thursday in Chattanooga, Tennessee – our community, and one we have loved for over twenty-five years.”

CNN law enforcement analyst Tom Fuentes said depression doesn’t necessarily make anyone more likely to kill.

“I think mental health professionals would be not happy with what the parents are assessing, in saying, ‘Well, he was depressed, and therefore that’s why he became a killer like this,’” Fuentes said. “People with depression do not turn, necessarily, into psychopathic killers – as he did.”

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Beefing up security

In response to the shootings, some governors have taken steps to increase the security of National Guard recruiters and military facilities in their states.

States control their National Guard units, so governors can make decisions about Guard actions, whereas the president is commander in chief of the nation’s military branches.

Under Florida Gov. Rick Scott’s order, National Guard members at six state recruitment centers will be relocated to armories until security is improved. In addition, law enforcement agencies will be asked to conduct regular security checks and qualified Guard members will be adequately armed, according to a statement from the governor’s office.

“We’re going to do everything we can to make sure all of our Guardsmen are safe,” Scott told CNN. “We’ve got to understand that we have people in our country that want to harm our military.”

Texas Gov. Greg Abbott’s order will arm National Guard personnel at military facilities throughout the state.

Oklahoma Gov. Mary Fallin authorized the arming of certain full-time personnel in military installations throughout the state. “It is painful enough when we lose members of our armed forces when they are sent in harm’s way, but it is unfathomable that they should be vulnerable for attack in our own communities,” she said in a statement.

“It is painful enough when we lose members of our armed forces when they are sent in harm’s way,” she said in a statement “But it is unfathomable that they should be vulnerable for attack in our own communities.”

Timeline: U.S. military recruiting center attacks, from New York to Chattanooga

Bergen: History of attacks against U.S. military installations

CNN’s Boris Sanchez and Aaron Cooper reported from Chattanooga and CNN’s Catherine E. Shoichet wrote the story in Atlanta. CNN’s Jomana Karadsheh, Holly Yan, Ashley Fantz, Joe Sutton, Ray Sanchez, Barbara Starr, Pamela Brown, Evan Perez, Danelle Garcia, Brian Todd, Joshua Gaynor, Shimon Prokupecz and Devon Sayers contributed to this report.