(CNN) One day after a deadly church shooting in Antioch, Tennessee, new details began to emerge about the suspected gunman's prior contact with police and his activity leading up to the shooting.

One person was killed and seven others injured Sunday as services were wrapping up at the Burnette Chapel Church of Christ near Nashville.

Emanuel Kidega Samson, 25, of La Vergne, Tennessee, was charged with felony homicide and was being held without bond. Other charges are coming later, police said Monday. He will appear in court on Wednesday.

Samson acknowledged he was at the church Sunday and that he opened fire, Nashville police said.

The Justice Department and FBI have opened a federal civil rights investigation into the shooting, and police said they are trying to establish the suspect's motive. Local police requested the assistance of the Bureau of Alcohol, Tobacco, Firearms and Explosives to run an "urgent trace" on a firearm, an ATF representative told CNN.

The trace would give authorities an indication of where the gun was purchased, who purchased it and whether it was purchased legally, the ATF representative said.

'Major chaos'

Danny Carter, a congregant at the church, described the scene.

"It was just major chaos. I didn't see the shooter until he came through the door. I basically hollered for people to get down and at that point the shooter was basically the only one up moving until Mr. Engel (the church usher hailed as a hero) saw him and confronted him."

Meanwhile, a community in mourning prepared for prayer vigils for victims and their families.

Nashville Mayor Megan Barry, speaking on Monday as she attended two vigils, called the community a "counterweight to grief" and pledged that her city would come together for the families of the victims.

"I want the people of Nashville to know that we are a community that lifts up others and this is what we're here to do tonight. At the moment this is about the families who were impacted."

At one of the vigils, friends and neighbors held candles shielded by red plastic cups and sang hymns as the sun set.

"This is obviously a horrific situation and right now we're dealing with the victims and their families," Carter said.

"I was glad that (the community came out). A lot of response from a lot of people who didn't know (the victims)."

Funeral services for Melanie Crow Smith of Smyrna, Tennessee, the 39-year-old victim in the shooting, will take place Wednesday and Thursday, according to an online posting from the West Harpeth Funeral Home and Crematory.

What we know about Samson

Police initially said Samson was African-American, but later identified him as Sudanese with legal US residency.

On Saturday, the day before the shooting, Samson worked a shift as a security guard for Crimson Security in Nashville, police spokesman Don Aaron said. He sent an email Sunday at 10:10 a.m., within an hour of the shooting, saying he appreciated the opportunity to work but would not be returning.

State records indicate Samson had held a liense to work as an unarmed security guard between 2014-2016, Nashville police said. It had expired, and Samson attended a class on Friday to reinstate the unarmed license.

Over the past year, police in the area encountered Samson on three separate occasions.

On June 27, Murfreesboro Police responded to the home of Samson's father after a 911 call reporting suicidal threats. His father told police that Samson had texted him shortly after midnight saying he had a gun to his head, according to a police report. Samson's father said he tried unsuccessfully to reach his son on the phone and did not know where he was.

Police pinged Samson's phone and found him at the Nashville office of security service provider G4S, Nashville Police said in a news conference Monday. Nashville Police officers met Samson at the office, dressed in professional business clothes. Samson told the officer that he was fine and not thinking of harming himself. The officer was satisfied that he was not a danger and left him.

Before the June incident, Murfreesboro Police responded to two domestic disturbance calls involving Samson and his former girlfriend.

In January, police responded to an address listed as Samson's home in Murfreesboro. During an argument, a woman told police that Samson punched her TV and broke a small figurine, according to a police report. They were fighting because he believed she had cheated on him, she told police. As she tried to leave the apartment, he demanded to speak to her and took her phone. She called police from a neighbor's home.

In March, police returned to the same home. Samson told police that he used to date the woman and that he was trying to break off contact with her but she "keeps coming around," a police report states. He said that, after a brief conversation at the door, she started to get loud and tried to push his door open as he tried to close it. Samson told police that he was in fear because "she has struck him in the past" but said she had not threatened or assaulted him that day. The woman told police she had come over to pick up some belongings and said she did not threaten or assault him.

Officers helped the woman retrieve her belongings and told her not to return to the apartment, the report states. Samson was told that he could no longer have contact with her.

From church parking lot to sanctuary

Samson told police that he had attended the church, but not recently. Church members confirmed this, telling police he attended the church one to two years ago, but that they had not seen him in a while and did not immediately recognize him because the gunman was masked.

A few members of the congregation, who declined to give their names because they did not want to speak for the church beyond its official statement, recalled Samson fondly. They said they were surprised to hear he may have been involved in something like this. He was friendly to everyone, they said, including one of the people he allegedly shot.

Samson pulled into the church parking lot in a blue SUV and is believed to have waited there for several minutes before church let out, police said in a statement.

Samson shot and killed Smith in the parking lot as she was walking to her car, police said. She died at the scene.

Carrying two pistols, the shooter then entered the church through the sanctuary's main door and "began indiscriminately shooting," said Aaron, the police spokesman. About 50 people were inside.

The gunman was silent when he opened fire, said parishoner Minerva Rosa, who was inside the church when the shooting started.

The shooting today at Burnette Chapel Church of Christ is a terrible tragedy for our city. Full statement: https://t.co/vk6DOxuMPc pic.twitter.com/x3UsUPDmA9 — Megan Barry (@MayorMeganBarry) September 24, 2017

Usher called 'a hero'

Six people, ranging in age from 64 to 84, were wounded by gunfire, Aaron said. One patient at Vanderbilt University Medical Center is in critical condition, the hospital said.

Church usher Robert Caleb Engle, 22, saw the shooting and confronted the gunman. During a struggle, Engle was pistol-whipped and the gunman mistakenly shot himself.

"The wound sent Samson to the floor. Engle, despite his head injuries, ran out to his car in the parking lot and retrieved a pistol. He held Samson at gunpoint until police arrived," a police statement said.

Police recovered four firearms believed to be Samson's -- two pistols in the church and a pistol and rifle from his SUV.

Nashville Police Chief Steve Anderson called Engle a hero who "stopped this madness so we're very, very, very grateful to him."

On Monday night, Mayor Barry echoed the sentiment.

"(Caleb) won't call himself a hero but I'm going to call him a hero. Without him who knows what would have happened inside these walls."

In a statement, Engle said he did not want to be labeled a hero.

"I've been going to this church my whole life, since I was a small child," he said. "I would have never, ever thought something like this would have happened."

He asked for prayers for the victims and their families.

"Please pray for the shooter, the shooter's family and friends. They are hurting as well," he said.

"The real heroes are the police, first responders and medical staff and doctors who have helped me and everyone affected."

Community prayers

Gunman opens fire at Church of Christ Burnette Chapel on Pin Hook Road. 1 woman dead in parking lot...6 other innocents shot... pic.twitter.com/yuwjfGPjXs — Metro Nashville PD (@MNPDNashville) September 24, 2017

Prayer vigils were held Monday to show support for the victims and their families: one at Woodmont Hills Church in Nashville, and another outside the Burnette Chapel Church of Christ.

"We are beyond grateful for the enormous outpouring of love and compassion we have received from so many after the tragic event that took place yesterday," the church said on its Facebook page Monday.

"We ask for your continued prayers and support during the coming days and months."