NEW YORK — One was an exemplary police officer, a veteran detective with an easy smile, a gift for talking to people and a deep knowledge of the characters in his precinct, on both sides of the law. He had made hundreds of arrests.

The other longed to be a police officer when he was young, but evolved instead into the sort of neighborhood nuisance police often have to deal with. At best quirky, and at worst emotionally disturbed, he amassed a long record of petty crimes, including impersonating a police officer. But recently, police said, he had started robbing cellphone stores.

The paths of the two men crossed at a T-Mobile shop in Queens last week. The veteran detective, Brian Simonsen, was among eight officers who responded when someone spotted a man forcing two employees into the store’s back office with a pistol.

Moments later, Christopher Ransom, 27, emerged and pointed what turned out to be a fake gun at officers, jerking it as if he were firing, the police said.

For 11 chaotic seconds, the police opened fire. Ransom and Simonsen were both hit in the police fusillade. Only one would survive the night.

“Make no mistake about it — friendly fire aside — it is because of the actions of the suspect that Detective Simonsen is dead,” the police commissioner, James P. O’Neill, said later that night at Jamaica Hospital Medical Center. The detective was 42 years old.

Sgt. Matthew Gorman was also wounded in the crossfire. Ransom’s accomplice and lookout man, Jagger Freeman, sprinted away, only to be arrested several days later, police said.

Had they met under different circumstances, friends of the detective said, Simonsen’s skill at calming down troubled people, coupled with Ransom’s desire to connect with the police, might have led to a less tragic outcome.

Instead the Police Department will lay to rest on Wednesday one of its most well-regarded veterans, killed by friendly fire, as Ransom faces life in prison, charged with causing his death.

‘A cop’s cop’

Simonsen, who had spent almost 19 years on the force, did not always want to be a police officer, his friends said. He felt a calling to help people through traumatic times, driven in part by the untimely deaths of his father and sister during his high school years.

He grew up in Riverhead on Long Island and studied social work at Roger Williams University in Rhode Island, where he also played catcher for the school’s baseball team. He worked in the social services field briefly before deciding to enter the New York Police Academy.

Law enforcement proved an excellent fit for an athletic and affable man interested in psychology. Simonsen began his career patrolling the 102nd Precinct in October 2000.

He was among the first to respond to the Sept. 11 terrorist attacks with Officer Terrence LeGrady. It was an ordeal that made the patrol partners inseparable. Years later, Simonsen would buy the house next to LeGrady’s in eastern Long Island.

In 2006, Simonsen joined the precinct squad, where he became an expert on robbery cases.

He and his partner at the time, Kevin O’Hea, were a fixture in the second-floor detective offices at the precinct, known for trading friendly banter with other officers and planning outings to Mets games.

He spent his entire career in the 102nd Precinct, where he made 569 arrests and brought more than 130 felony indictments to the Queens district attorney’s office.

His colleagues said he had a knack for convincing suspects to confess and for bonding with victims.

“He had a very good way of putting people at ease,” Tim Shortt, an assistant district attorney in the Queens office, said of Detective Simonsen.

In one case, Shortt recalled, Simonsen was assigned to investigate a robbery that left a victim with a broken jaw. Simonsen succeeded in getting one of the suspects to confess and to incriminate his partner. He then coaxed a confession out of the partner and had the man confirm his identity by signing the back of his own wanted flier.

“He didn’t need a rubber hose to play a tough guy,” Shortt said. “He would have suspects laughing in the lineup room. He always acted decently toward them.”

Even in cases where he had DNA evidence confirming a theory and a witness identification of a suspect, Simonsen and his partner made a habit of trying to obtain a written confession.

“We’d go talk to the guy because we felt like we needed him to tell us he did it,” said O’Hea, who retired in 2014.

Though he loved the job, Simonsen, who was a union delegate, had told friends he planned to retire soon if he did not receive a promotion to detective second-grade, a rank he had been nominated to receive.

For younger officers in the precinct, Simonsen was an anchor. One officer described him as “a cop’s cop.”

“He knew the neighborhood, all the good guys, all the bad guys,” the officer said, speaking on the condition of anonymity because he was not authorized to talk to a reporter. “Whether you’re a rookie or you’re a senior guy, he treated you the same. You always wanted to talk to Brian.”

A police family on Long Island

That reputation as a community pillar extended to Calverton, Long Island, where Simonsen had settled with his wife Leanne, after meeting her on a trip to Las Vegas with mutual friends.

Their neighborhood parties were legendary, including a particularly large bash Simonsen threw last year for his grandfather’s 100th birthday.

Simonsen opted to make the 70-mile commute into the city rather than leave Long Island, where he played softball in the Riverhead police league.

Though Simonsen and his wife never had children, they kept the fridge stocked with snacks for the neighborhood kids. He had recently given his childhood baseball mitt to LeGrady’s son, who also loved the game. His friends’ children called him Uncle Brian.

His sister-in-law, Michelle Quinn, said Simonsen had a deep love not just for his wife, but for her entire family in Chicago, which includes several police officers. “It was so easy to see the love between him and my sister,” she said.

Quinn recalled how she had once admired her brother-in-law’s New York Islanders sweatshirt during one of his trips to Chicago. After he returned to New York, she found it in her house.

“He left it for me, with a note,” she said. “Truly gives you the shirt off his back.”

“The guy robbing the store,” Quinn added, her voice breaking. “Brian would have bought him a cellphone. He would have put him on his plan.”

‘He would go a little cuckoo’

In the days since the shooting, police officials have described Ransom as a career criminal. For those who knew him, that description is not wrong, but does not tell the whole story, either.

Ransom has been in and out of trouble with the law since 2010, with 25 arrests as a juvenile and an adult. Still, his adult criminal record does not include any violent crimes or involve weapons. His most serious convictions were for shoplifting. His other convictions were for actions that were more bizarre than menacing.

“That’s what was kind of mind-boggling to me, to even see that he was in that situation,” said Larry Davis Nedd, a deacon at Brooklyn’s New Grace Tabernacle Christian Center, where he knew Ransom in his young-adult years.

Friends, family and longtime neighbors of Ransom described a man of contrasts, prone both to deep displays of charity and to intense flashes of instability. He had trouble finding work.

The one constant in his manic existence was a fascination with law enforcement and the criminal justice system, they said. Since he was a boy, Ransom had desperately wanted to become a police officer, recalled Frank Rios, a lifelong friend. But Rios said questions about Ransom’s mental health kept him from pursuing the job.

Rios was not the only associate of Ransom’s who recalled emotional and mental health problems. Neighbors of Ransom’s mother in Ocean Hill, who had adopted him out of foster care, recalled her frustration with his tendency to act out in odd ways. She had taken him to counseling and had gotten him medication, one neighbor, Clemente Williams, said.

“He wouldn’t take his meds and his mother would say he would go a little cuckoo,” Williams said. “He seemed to be an all-right guy but a little off.”

Ransom’s sister, Patricia Rush, 46, also recalled that Ransom took medication for a mental condition as a child and was supposed to continue taking it into adulthood, though she did not recall what disorder he had. “He is supposed to be on medication right now,” she said.

Quirks that appeared innocent in childhood grew darker and more serious as Ransom matured. After he failed to pursue a career as a police officer, he went to peculiar — and sometimes illegal — lengths to make inroads in the city’s justice system. He was prone to wearing fake policing gear in public. He donned it one morning in 2016 as he tried to nonchalantly enter Brooklyn’s 77th Precinct offices.

Wearing a tactical vest and a fake badge that read “Super Police,” Ransom tried to gain access to restricted areas of the building. He was arrested, convicted of impersonating a law enforcement officer and spent 20 days in jail.

Ransom was also convicted in 2012 of fraudulently claiming to be a college intern in order to gain access to restricted areas of the Kings County courthouse, including judges’ chambers.

He was later convicted of criminal trespass and issued a protective order that forbade him from contacting two judges in the building. Court records show he violated that order the following year.

In recent years, Ransom’s behavior spiraled erratically. He left his church, moved out of his old neighborhood and became estranged from friends and family, including his sister. Known as a prankster in childhood, Ransom began engaging in stunts aimed at gaining notoriety on the internet, his sister said. He posted some of his antics on his YouTube channel, tagged under “Christopher Ransom Productions.”

In one 2016 post, Ransom can be seen wearing nothing but underwear and a cape, walking into a police station and thanking officers for their service.

“I love you guys and I appreciate the NYPD,” he said, before leaping toward the exit.

Whatever aspirations Ransom had in his youth, there were signs in recent days that he had abandoned hope of a normal life. On Jan. 17, he took to Facebook to voice frustration. “It took me 27 years to realize that I’m not a job type of dude,” he wrote.

Two days later, the police said, Ransom was caught on a security camera as he robbed a cellphone store in Jamaica, Queens, holding a black handgun similar to the fake one he dropped when he was shot on Feb. 12.

On Feb. 8, Ransom teamed up with Freeman, 25, to rob a T-Mobile store in the St. Albans neighborhood, brandishing a firearm and making off with about $1,000 and 25 iPhones, according to a criminal complaint.

A tragic shooting

Ransom’s last social media update, posted the afternoon of Feb. 12, is a photo of himself in a trench coat, leaning against a bar with a bottle of Hennessy cognac. There is no description or caption.

Five hours later, as rain and sleet coated the streets of Richmond Hill, Queens, Ransom and Jagger arrived in a car at the T-Mobile store on Atlantic Avenue at 120th Street, police said. Ransom went in while Jagger stood watch outside, according to a criminal complaint.

Just a few blocks away was Simonsen, who had decided that night to go out on a shift, even though he had attended a union meeting earlier and was not required to work. He was eager to continue investigating a pattern of robberies with his supervisor, Gorman, the police said.

It was supposed to be a quiet night, polishing up reports and preparing for an upcoming review from headquarters. Neither the detective nor the sergeant were wearing bulletproof vests, the police said.

Still, when the report came over the radio at 6:09 p.m. of a robbery at the T-Mobile store, the pair responded. They arrived at the same time as a patrol car.

Gorman, as the highest-ranking officer at the scene, entered the shop with two patrol officers to confront Ransom, who had already stuffed a duffel bag with cash. He had taken two employees into the backroom of the store and demanded that they open a safe containing iPhones, when officers entered, according to police officials and two criminal complaints.

Ransom came out of the backroom holding up an authentic-looking imitation of a Colt pistol, court papers said. He advanced toward the door as officers backed out of the shop. As he approached the door, he raised a gun and made a motion to shoot.

Police would later determine that the ensuing eruption of gunfire was from seven officers firing 42 bullets. Eight of them hit Ransom, who fell inside the store, his fake gun nearby. One wounded Gorman in the thigh. Another mortally wounded Simonsen, striking his vest-less chest.

Twenty-four hours later, Ransom, who once dreamed of becoming a police officer, would be accused of causing the death of one. Ransom and Freeman have both been charged with murder.

And from Chicago to the eastern reaches of Long Island, the beloved officer’s friends and family members would be struggling to grasp how a quiet night went so horribly wrong.

“Brian was such a fun jokester, I’m hoping somehow it’s a big joke,” Quinn, his sister-in-law, said.

“Just know he was the best.”

This article originally appeared in The New York Times.