Chattanooga, Tennessee (CNN) Chattanooga shooter Mohammad Abdulazeez told a friend that ISIS was "doing wrong" and "it was a stupid group and it was completely against Islam," the friend told CNN on Monday.

The friend, James Petty, also said that Abdulazeez taught him how to shoot an AR-15 assault rifle and that the two would practice in the woods.

The revelations about Abdulazeez came as sources told CNN that writings uncovered by investigators indicated Abdulazeez was displeased with the U.S. government, particularly its war on terror.

The writings are not thought to be recent -- some are more than a year old, predating his much-publicized trip to Jordan -- and should not be considered a diary of any sort, according to a person familiar with the family's interviews with investigators and a law enforcement official briefed on the investigation.

The writings also include other anti-U.S. sentiments and are consistent with someone who is having suicidal thoughts, the sources said.

Photos: Deadly shooting in Chattanooga, Tennessee Photos: Deadly shooting in Chattanooga, Tennessee An FBI investigator works outside a military recruiting center where a gunman opened fire Thursday, July 16, in Chattanooga, Tennessee. Authorities say Mohammad Youssuf Abdulazeez, 24, opened fire first on the recruiting station and then moved to a U.S. Navy facility seven miles away. At the Navy facility, he fatally shot four U.S. Marines and wounded three other people before he died in police gunfire. A U.S. Navy sailor later died from his wounds. Hide Caption 1 of 12 Photos: Deadly shooting in Chattanooga, Tennessee Abdulazeez was born in Kuwait and had Jordanian citizenship, law enforcement officials said. He was a naturalized U.S. citizen. Hide Caption 2 of 12 Photos: Deadly shooting in Chattanooga, Tennessee A woman places a balloon and flowers at a makeshift memorial outside the military recruiting center on Friday, July 17. Hide Caption 3 of 12 Photos: Deadly shooting in Chattanooga, Tennessee The Rev. Drew McCallie prays during a church service in Chattanooga on July 16. Hide Caption 4 of 12 Photos: Deadly shooting in Chattanooga, Tennessee Members of the FBI gather evidence at the scene of the recruiting center shooting on July 16. Hide Caption 5 of 12 Photos: Deadly shooting in Chattanooga, Tennessee A police car blocks the entrances to the U.S. Navy Reserve Center on July 16. Hide Caption 6 of 12 Photos: Deadly shooting in Chattanooga, Tennessee A car believed to be driven by Abdulazeez is seen on the grounds of the Navy facility. Hide Caption 7 of 12 Photos: Deadly shooting in Chattanooga, Tennessee WTVC's Drew Bollea heard gunshots on Amnicola Highway near the Navy facility. Hide Caption 8 of 12 Photos: Deadly shooting in Chattanooga, Tennessee The gunman first opened fire at this military recruitment office located in a strip mall off Lee Highway in Chattanooga. Hide Caption 9 of 12 Photos: Deadly shooting in Chattanooga, Tennessee The entrance to the military recruiting office is seen riddled with bullet holes on July 16. Hide Caption 10 of 12 Photos: Deadly shooting in Chattanooga, Tennessee Blue evidence markers, believed to be the location of spent shell casings, can be seen here. Gina Mule, a server at a restaurant who took this photo, said she saw a man in a car firing a "high-powered rifle" at the recruiting offices at about 10:50 a.m. ET Thursday. Hide Caption 11 of 12 Photos: Deadly shooting in Chattanooga, Tennessee An officer patrols the parking lot of the recruitment center. Hide Caption 12 of 12

As the country mourns the deaths of five service members gunned down Thursday in Tennessee, investigators in both the United States and Jordan are trying to learn what prompted the attack.

Abdulazeez first shot up a military recruiting center at a Chattanooga strip mall, then drove to a local Navy operations support center and launched another attack, killing four Marines and a sailor. Abdulazeez died in a gunfight with law enforcement.

New details have emerged over the past few days. Among them:

• Abdulazeez suffered from depression and "was not the son we knew and loved," his family said in a statement over the weekend. "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." A police officer was among the wounded.

• The family has also told investigators the 24-year-old had been abusing drugs for some time, according to a source familiar with the family's interviews with investigators. The drugs reportedly included "party drugs" and marijuana. Petty, Abdulazeez's friend, told CNN that his buddy had a drug problem and used marijuana heavily, to the point that his parents were constantly calling to check on his whereabouts.

• Abdulazeez's family sent him to Jordan last year to get him away from Chattanooga friends who they said were bad influences on him, the relatives told investigators. According to a family representative who asked for his name not to be used, Abdulazeez's parents sent him to Jordan to stay with a family, with the hope of getting Abdulazeez away from his life of depression and drug use in Tennessee.

• Some relatives and friends told investigators they detected changes in his behavior after he returned from Jordan last year, a law enforcement official said.

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

• Authorities are investigating a text message from Abdulazeez to a friend before the attack, law enforcement sources said. The message included an Islamic verse that says, "Whoever shows enmity to a friend of mine, then I have declared war against him."

• Abdulazeez had a hard time keeping a job because of his manic depressive/bipolar disorder and drug use, for which he had sought treatment with a psychiatrist, according to the source familiar with the family's interviews.

• "It grieves us beyond belief to know that his pain found its expression in this heinous act of violence," the Abdulazeez family said in its statement.

• Abdulazeez's parents knew their son owned guns and wanted him to give them up, according to the family representative. He allegedly refused, saying he was an adult. Abdulazeez's parents also tried to get him to seek substance abuse treatment, but he refused that also, the representative said.

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"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,' " CNN law enforcement analyst Tom Fuentes said. "People with depression do not turn, necessarily, into psychopathic killers -- as he did."

U.S. Attorney Bill Killian said the shootings are being investigated as terrorism.

So far, 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. Abdulazeez was not on any U.S. databases of suspected terrorists.

Boosting security

Some governors are increasing security measures for National Guard recruiters and military facilities. Several have called for arming National Guard members.

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Florida Gov. Rick Scott ordered National Guard members at six state recruitment centers to be relocated to armories until security is improved. In addition, qualified Guard members will be armed.

Texas Gov. Greg Abbott has called for armed National Guard personnel at military facilities throughout the state.

And 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," she said in a statement. "But it is unfathomable that they should be vulnerable for attack in our own communities."

Grief across the country

The victims came from across the country , but united in Chattanooga, brought together by their service in the military.

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Marine Gunnery Sgt. Thomas Sullivan of Massachusetts was a two-time Purple Heart recipient. He served three tours of duty.

Lance Cpl. Squire K. Wells, better known as "Skip," graduated from high school three years ago. The Georgia native joined the Marines in 2014 and had already earned a National Defense Service Medal.

His mother told CNN's "Anderson Cooper 360" that her son had always wanted to be a Marine.

"Skip was friends with everybody," Cathy Wells said. "He was going to make sure that everybody got out before him. That's always how he's been."

Marines Staff Sgt. David Wyatt of Arkansas served two tours of duty in Iraq and one in Afghanistan. His wife posted about his death on Facebook. "He was such a great husband and father," one commenter wrote.

Marines Sgt. Carson Holmquist was also a husband and father and served two tours of duty in Afghanistan. Upon one of his homecomings, his family held up a sign that read, "We've waited 244 days for this moment. Welcome home Sgt. Holmquist."

Navy Petty Officer Randall Smith of Ohio was a logistics specialist. He saw the gunman in last week's attack and warned people around him, family members said, but was unable to get away.

On Sunday, Smith's mother visited a makeshift memorial for the victims. Paula Proxmire cried as she left a baseball glove, a baseball and an American flag in honor of her son.

Red, white and blue balloons covered the memorial, along with a poster with pictures of the victims.

About those flags ...

While many remained in mourning Monday, outrage arose via a bogus assertion that President Barack Obama failed to issue a proclamation to lower flags around government buildings to half-staff despite doing so for pop singer Whitney Houston.

Many on social media fell for the bait, even former pitching ace Curt Schilling, but there was no truth to it. Obama did not order the flags at half-staff for Houston's death.

Flags at half mast for Whitney Houston? 4 Marines and 1 Navy serviceman assassinated by a terrorist on our soil.....nothing? — Curt Schilling (@gehrig38) July 20, 2015

Gov. Chris Christie controversially ordered New Jerseys flags to half-staff for Houston, as he did for saxophonist Clarence Clemons of Bruce Springsteen's E. Street Band.

The last time there was a national call to fly the flags at half-staff was Memorial Day, the rules for which dictate keeping the flags at half-staff until noon. As for honoring people, the flags were last lowered in April, in commemoration of President Abraham Lincoln's death, and in December 2013, in honor of South Africa's Nelson Mandela.

Among the tragedies that have prompted the honor are the 2009 mass shooting at Fort Hood, Texas; the Sandy Hook Elementary School shooting in Newtown, Connecticut, in 2012; the 2012 attack on the U.S. Embassy in Benghazi, Libya; the Boston Marathon bombings in 2013; and the 2013 Washington Navy Yard shooting.

Flags are flown at half-staff on holidays such as Memorial Day, Patriot Day, Peace Officers Memorial Day and Pearl Harbor Remembrance Day. They're also lowered for the annual Fallen Firefighters Memorial Service.

Because of confusion over when to lower the flags, President Dwight Eisenhower in 1954 issued rules outlining the proper times to do so, according to the U.S. Department of Veterans Affairs. The flags are to be lowered at all federal institutions for the death of a present or former president, vice president, House speaker, Senate president pro tem, Cabinet member, Supreme Court justice and other high-ranking officials.

When a congressman dies, flags are flown at half-staff in Washington and in the state from where the lawmaker hailed. States also lower their flags at all of their federal facilities when a governor dies, the VA says.

"The President may order the flag to be flown at half-staff to mark the death of other officials, former officials, or foreign dignitaries. In addition to these occasions, the President may order half-staff display of the flag after other tragic events," the VA says.

For those pondering why Fort Hood would earn the honor but Chattanooga would not, that's not totally clear. It could be related to the Fort Hood shooting being deemed an act of workplace violence. A military jury in 2013 convicted Army Maj. Nidal Hasan in the rampage