The man facing murder charges in the shootings of five people in a Philadelphia neighborhood earlier this week "obviously planned" the rampage, but the investigation into other factors of the case could take months as authorities dig for more details, a district attorney said.

Authorities believe Kimbrady Carriker acted alone when he carried out the mass shooting Monday night, but investigators are still combing through his social media history as well as mental health concerns, Philadelphia District Attorney Larry Krasner told CNN on Wednesday.

"I can certainly tell you that there are indications of mental health issues. There are indications of irrational behavior. There are indications of irrational statements and irrational acts," Krasner told CNN.

Krasner's remarks come as new details emerged Wednesday about Carriker's possible motive behind the mass shooting in Philadelphia's Kingsessing neighborhood -- where five victims were killed, the youngest of whom is a 15-year-old boy.

Carriker, 40, allegedly told police, in sum and substance, that he carried out the shooting to clean up the neighborhood, two law enforcement sources told CNN.

The suspect's social media activity has also come under investigators' scrutiny. A deleted social media page believed to be Carriker's featured a series of posts about guns, the Second Amendment and the "loss of freedoms," according to a law enforcement source.

Hours before the Monday night shooting, a public post on the social media page showed a video advertisement for a tactical weapons accessories company. The video, posted at 10:49 a.m. ET, shows a man in tactical gear, holding what appears to be a military-style rifle.

Initial reports of the shooting came around 8:30 p.m. Monday, authorities have said. Officers eventually arrested Carriker in an alley after a chase on foot. Donned in a bulletproof vest and ski mask, Carriker also had an AR-style rifle, a 9 mm handgun and a scanner that tracks emergency response radio traffic, authorities said.

Suspect arraigned on Wednesday

Krasner, who is the lead prosecutor in the case, noted investigators see "all kinds of indications of premeditation" in how the weapons were purchased and the clothing that was worn during the shooting.

"But when you get into issues of psychological state, motivation, intent beyond the obvious, which is that he obviously planned this ... that can be a monthslong process," Krasner told CNN.

That process includes going through cell phones, social media, using high level technology and extensive interviews to try to learn more about the shooting, Krasner explained.

Meanwhile, Carriker was arraigned Wednesday on charges of murder, attempted murder, assault, reckless endangerment and weapons charges, and he was ordered held without bail. He was not required to enter a plea.

The gunman is suspected of killing Daujan Brown, 15; Lashyd Merritt, 20; Dymir Stanton, 29; Ralph Moralis, 59; and Joseph Wamah Jr., 31, police said. Wamah's body was found in a home early Tuesday, while the others were found Monday night, authorities said.

The Philadelphia Public Defender's Office, which is representing Carriker, said it would not comment on the case at this time.

The shooting was one of least 350 mass shootings in the US so far this year, according to the Gun Violence Archive. CNN and the archive define a mass shooting as one in which four or more people are shot, not including the shooter.

The tragedy in Philadelphia unfolded on the heels of another shooting in Fort Worth, Texas, on Monday night when at least three people died and eight were wounded. On the same day, a 16-year-old girl was killed and four other people were injured in a shooting at a Monday night block party in Indianapolis. Two others were killed and 28 were injured in a shooting in Baltimore the day before.

Suspect's behavior prior to shooting under scrutiny

Prior to the shooting in Philadelphia, witnesses said Carriker had been acting oddly and displayed "abnormal behavior for quite a while," Philadelphia Assistant District Attorney Joanne Pescatore said during a news conference Wednesday.

People who lived in the same house as Carriker said "he was getting more and more agitated as the days were passing," Pescatore said.

Carriker had also written a will in his own handwriting and dated it June 23, which investigators recovered from home while executing a search, according to Assistant District Attorney Bob Wainwright. The will did not include any plans to carry out the shooting, Wainwright noted.

Investigators also found a .380-caliber handgun, ammunition and live rounds that matched ammunition found at the scene of the shooting, Wainwright added.

Meanwhile, the suspect's social media history revealed that he shared posts from pro-gun groups supporting former President Donald Trump and the Second Amendment.

Last month, he shared a mocking video of a speech by President Joe Biden and added his view that Biden was trying to "take our arms." Another post from the same day says, "The only thing more terrifying than blindness is being the only one who can see."

The page also has references to God and prayer posted over the last week, including a passage from the book of Isaiah posted by Carriker that begins, "I alone am the Lord, the only one who can save you." Another post quotes Nehemiah: "But we prayed to our God and guarded the city day and night to protect ourselves."

In one post, he complained about what he believed was a loss of freedom. And in a repost this week, he pinned a quote that read, "So often we accept the loss of freedoms in the name of safety. But we never feel any safer and we never get the freedoms back."

In a June 20 post, he said of crime in the community, "During community patrols I have notice a big shame. So many of our 50 + 60 + 70 year old elders are influencing the youth negatively. They are without a doubt promoting and participating in robbing, prostitution, scamming, and murder."

Another post on Carriker's Facebook page shows photos of armed protesters dressed as Black Panthers taken at a 2020 Atlanta protest. He also shared that they were "exercising their first and second amendment" rights.

Community is traumatized, mayor says

Philadelphia Mayor Jim Kenney told CNN on Wednesday the Kingsessing neighborhood where the deadly mass shooting occurred is traumatized.

"They're traumatized, and obviously, rightfully so. There's no reason in the world that that situation should have happened Monday night," Kenney told CNN's Jake Tapper. "And the common denominator in all of these things are guns, and the availability of guns and the high capacity of guns."

In addition to the five killed, two boys, ages 2 and 13, were each shot in the leg and were in stable condition, police said. A 33-year-old woman and another 2-year-old boy were injured by glass, authorities said.

The two 2-year-old children are twins who were in a car with their mother when shots were fired at them, authorities said.

Referring to the Second Amendment, the Democratic mayor said, the Founding Fathers "weren't talking about AR-15s to mow down people in the streets of Philadelphia."

Kenney's comments came as officials revealed Wednesday that the AR-style rifle and 9 mm handgun found in Carriker's possession were privately made weapons known as ghost guns, according to Philadelphia Police Deputy Commissioner of Investigations Frank Vanore.

The firearms didn't have any markings and are not traceable, Vanore added.

Ghost gun confiscations in the city have increased 300% in the past three years, Kenney noted.

Kits from which the guns are made are sold online without the buyer needing a background check and without serial numbers on the parts, he said.

"This is like a level of insanity that no one should ever deal with," Kenney said.