In the hours after he was taken into custody, a picture began to emerge of Scott Michael Greene, 46, through court records, police statements and social media postings. On at least two occasions — including one just weeks before the shootings — Greene apparently was involved in tense, racially infused confrontations.

Sgt. Anthony Beminio and Officer Justin Martin were shot and killed early Wednesday morning in a pair of “ambush-style attacks,” the Des Moines Police Department said. Within hours, officials identified Greene as the lone suspect in the deaths of Beminio, a Des Moines officer, and Martin, who worked in Urbandale, a neighboring city.

Police described Greene, an Urbandale resident, as armed and considered dangerous and warned residents to call the authorities if they saw him. Greene was apprehended shortly before 9 a.m. when he was walking down a rural road and flagged a person out working on their tractor, asking them to call 911, according to authorities.

When the Dallas County Sheriff’s office and Iowa State Patrol responded, the man identified himself as Greene and said he had “an existing medical condition that was flaring up,” Sgt. Paul Parizek, a Des Moines police spokesman, said in an interview.

Greene was then brought to a hospital and is in police custody there, Parizek said. He is not under arrest because he has not been charged yet, Parizek added.

Police say they do not believe anyone else was involved, and officials say they are investigating whether the shooting was related to a confrontation involving police at a school last month.

Authorities in Des Moines, Iowa’s largest city, appeared shaken by the double shooting, which came during a year that has seen bloody attacks on officers in cities including Dallas and Baton Rouge, assaults that have fueled a sense of anxiety among law enforcement nationwide. In Des Moines, police were ordered to patrol in pairs Wednesday for safety.

During a news briefing, Parizek said it did not appear there was any interaction between the officers and “the coward . . . that shot them while they sat in their car.” Parizek then briefly choked back emotion as another officer reached a hand out to show him support.

Parizek said later Wednesday morning that authorities did not know what might have motivated the shooting, and he noted that “we may never know what motivated this act.” He said everyone involved — both officers and the suspected attacker — are white.

One of the officers was fatally shot next to Urbandale High School. A video uploaded to YouTube last month by an account bearing Greene’s name was titled “Police Abuse, Civil Rights Violation at Urbandale High School” and recorded a person arguing with police officers asking him to leave the area.

The man recording the footage is identified by an officer as Greene. In this video, the man can be heard telling the police he was assaulted and almost mugged while “peacefully protesting” at what appears to be a high school. An officer is later seen explaining that the Confederate battle flag he was waving violated the school’s code.

“In the current social climate that we’re in, when you fly a Confederate flag standing in front of several African-American people, that’s going to cause a disturbance, whether you intended to or not,” the officer said. As a result, the officer said, this man was no longer allowed on the school’s property.

The same night that Greene apparently flew the Confederate flag at Urbandale High, a predominantly white school, Urbandale’s football team crushed Hoover High of Des Moines 61-13.

Another video posted by the same account showed a still image of a man holding a Confederate flag in what appears to be the stands outside athletic event.

Denzil Miller, a Hoover High senior, said a “murmur” spread along the Hoover sideline as people noticed Greene’s Confederate flag, the latest in a series of recent incidents involving Iowa schools and that flag.

“It was kind of shocking,” said Miller, 18. “It’s not like everyone was getting into a big uproar about it, but everyone noticed.”

A spokeswoman for the Urbandale school district said the altercation took place at a high school football game and involved a man with Greene’s name, but she was not sure if it was the same person. Parizek said police were aware of this incident but were not going to discuss it further “until we understand if it’s valuable to the investigation.”

The Urbandale Police Department said that they had issued a warning to Greene for the episode. Police also said his daughter attended the school. Court papers say that Greene has a daughter with the same name as a student listed on a roster for the school’s cheerleading squad.

Police said Wednesday that Greene had been “known to law enforcement.” Court records show that a man with Greene’s name had a history of run-ins with police, including charges of assault and harassment, some of which were dismissed.

In 2014, court records show that Greene was convicted after being accused of harassment. A man in that case told police that Greene called him the N-word and threatened to kill him. Two days earlier, police said Greene was “hostile” and “combative” when officers tried to pat him down for a weapon, though they did not write in the affidavit why they wanted to search him other than that he “was known to go armed.”

Another, more recent case involved Greene accusing his mother of domestic abuse while he was living in her home.

According to court documents, police say Greene recorded an altercation with his mother two days after the incident at Urbandale High School. An officer said that Greene produced a video showing his mother yelling at him, grabbing him and hitting him.

Neighbors said that since that altercation, Greene’s mother had moved out and he had begun to act strangely. Last week, he saw Richard “Doc” Nance and Phyllis Nace, who have lived across the street for about a year, and walked over and hugged them without warning.

“From the first time I met him, just sometimes you look at a person and the lights are a little dim,” said Richard Nance, 73. Still, he said he never thought “he would kill a couple of cops.”

The Nances said they saw Scott begin moving things out of the house in recent days, and on Wednesday morning, they saw two of his daughters and one of their mothers arrive with a U-Haul to move things out.

Police arrived and told them to stop, the Nances said.

The killings early Wednesday shuttered schools in the area and launched law enforcement officers from multiple agencies into a sweeping, hours-long hunt for Greene.

Democratic presidential nominee Hillary Clinton’s campaign said that due to the shooting, it was canceling an event planned for Wednesday night in Des Moines with Tim Kaine, her vice-presidential running mate, and former president Bill Clinton, her husband.

Clinton wrote on Twitter that she was “heartbroken” for the families of the officers, while Donald Trump, Clinton’s Republican opponent, posted on Twitter that an attack on police “is an attack on us all.”

The White House said officials had been in touch with local authorities about the shooting. In a statement, Attorney General Loretta E. Lynch decried the shootings, calling them “yet another reminder of the tremendous dangers that law enforcement officers face each and every day.”

She also referred to the tension felt between police and communities of color, unease that has flared up during regular protests in recent years over how police officers use force.

“I know that this is a time of particular tension and mistrust between law enforcement and many communities,” she said. “I know that while we do not yet know what led the perpetrator to commit these awful crimes, many will be nevertheless be tempted to read a message or motive into this assault. But let me be clear: there is no message in murder.”

The first shooting in Iowa occurred at 1:06 a.m. when an officer in Urbandale, which is part of metropolitan Des Moines, responded to a report of shots fired, Parizek told The Washington Post.

That officer was shot while sitting alone in his patrol car at 70th Street and Aurora Avenue, next to Urbandale High School. He was pronounced dead on the scene, Parizek said.

Urbandale Police Chief Ross McCarty identified that officer as Justin Martin, who he called “a very good young man” who had just joined the department a little over a year ago.

Martin was hired in August 2015, graduated from the police academy last December and had only emerged from his probationary period in August and was turned into a one-man unit. He was killed just 10 weeks later.

About 20 minutes after Martin was shot, Des Moines police responding to that shooting came across a patrol car at Merle Hay Road and Sheridan Drive, an intersection about two miles away, where they found another officer with a gunshot wound, according to Parizek.

Sgt. Anthony Beminio of the Des Moines police was transported to the Iowa Methodist Medical Center, where he was also pronounced dead.

Police described both shootings as sudden, violent ambushes.

“It doesn’t appear that either officer had an opportunity to interact with the suspect,” Parizek said. “It doesn’t look like there was an exchange of conversation. There definitely wasn’t an opportunity for these officers to defend themselves . . . Both officers were seated in their cars and were shot while they were sitting.”

Parizek described the situation as “a clear and present danger to police officers” during the manhunt.

Both Martin and Beminio graduated from Simpson College, school officials said Wednesday. Beminio graduated in 2001 and Martin followed four years later, both with criminal justice degrees, the college said.

“The loss of any police officer in such a senseless act of violence is a tragedy,” Simpson President Jay Simmons said in a statement. “This is almost too much to bear. We all extend our deepest sympathy to the families of Anthony and Justin. We consider them part of our family, too.”

The shootings were the latest tragedy to strike the Des Moines police, coming just months after two officers transporting a prisoner were killed by a drunk driver traveling the wrong way down an interstate.

During an interview and news briefings, Parizek said that police around Des Moines were conscious of the tensions between law enforcement and citizens nationwide, even as he said there was not “a lot of that hatred of police here in this community.”

But he said officers were shocked by what unfolded early Wednesday.

“We absolutely did not think it was going to happen here,” he said.

The Urbandale Community School District canceled all classes Wednesday “per the recommendations of Urbandale and Des Moines law enforcement,” school officials said in a statement. They also asked staffers not to report to work.

The Des Moines public school system said that it would have school on Wednesday, a decision made after consulting with the city’s police chief.

“An attack on public safety officers is an attack on the public safety of all Iowans,” Gov. Terry Branstad, R, and Lt. Gov Kim Reynolds, R, said in a joint statement. “Our thoughts and prayers go out to the families of the police officers who were tragically killed in the line of duty as well as the officers who continue to put themselves in harm’s way.”

Through Wednesday, there have been 52 officers shot and killed in the line of duty this year, according to preliminary statistics from the National Law Enforcement Officers Memorial Fund, a nonprofit that tracks police deaths.

In a report covering the first half of the year, the fund said that more than half of the officers fatally shot by suspects were shot in ambushes.

While the number of police officers killed by suspects declined last year, that tally has already increased so far this year. In some cases, officers have been killed in high-profile incidents, including ambushes in Dallas and Baton Rouge in July that left eight police officers dead. These killings also occurred at a time of intense national focus on fatal shootings by police officers, incidents that have prompted protests of law enforcement that, in turn, have caused officers to say they feel vilified and uneasy.

Police also expressed concerns about ambushes and attacks after two pairs of officers were killed during incidents in 2014, first in Las Vegas and then New York.

The Des Moines officer who was slain appears to be the first from that city fatally shot in the line of duty since 1977, according to the police department’s website and records kept by Officer Down Memorial Page, another group that tracks such deaths.

The Washington Post’s Colby Itkowitz in Des Moines and Julie Tate, Alice Crites, Emma Brown, Derek Hawkins, Abby Ohlheiser, J. Freedom du Lac and Ben Guarino in Washington contributed to this report.