Santa Fe, Texas (CNN) A shooting at a Texas high school lasted for a terrifying 30 minutes on Friday. For 25 of those minutes, officers and the gunman engaged in a gunfight, Galveston County Sheriff Henry Trochesset told CNN Sunday.

The first shots were fired not long after classes began around 7:30 a.m. (8:30 a.m. ET), officials said. Officers arrived to the Santa Fe High School art lab section about four minutes into the shooting, Trochesset said, and engaged the shooter right away.

A total of 10 people -- eight students and two teachers -- were killed and 13 were injured as a result of the shooting. Dimitrios Pagourtzis , 17, was identified as the shooter. He was armed with a shotgun and a .38 caliber handgun.

When asked whether all of the victims were shot by Pagourtzis, Trochesset said authorities will have to learn that after the medical examiner autopsies are complete.

There is a "decent amount of cameras in the school," Trochesset said, so a lot of video does exist. Investigators are going through all of the video and putting together a timeline, Trochesset said.

Officials mourn with families, speak at Baccalaureate

Texas Gov. Greg Abbott attended church on Sunday to pray and mourn with the families who lost loved ones and to pledge action, just two days after a school shooting.

"We pray that God heal the hearts of the parents who have lost a child," Abbott, speaking to reporters after the service, said. "We pray that those who suffered these horrific injuries will meet with swift healing and repair. We pray for all the kids who attend this school for the nightmare that they lived through."

Abbott also offered plans of "swift" action for the coming days, primarily a Tuesday roundtable to discuss next steps in protecting students and schools from gun violence.

"But we know that, beginning this next week, it's time to go to work," he continued. "Go to work to make sure that this will be a catalyst to make sure this will be a pathway to reforms so that other students will not have to live through a nightmare like what these students had to go through."

The Sunday service took place at Arcadia First Baptist Church, attended by many families with children who go to Santa Fe High School. During the service, several senior Santa Fe High School students were honored for their coming graduation. But the focus remained squarely on Friday's mass shooting.

Galveston County District Attorney Jack Roady spoke at the Santa Fe High School Class of 2018 Baccalaureate program Sunday afternoon at a local church. Roady told the graduating students they were entering a "war zone."

"You are already dealing with the full effects of sin in our world," he said.

Roady encouraged students to find comfort in their belief in God so that they could comfort others.

One victim's story

One of the 10 people killed in the Texas school shooting was a girl who had rejected the suspect's advances for months, and stood up to him a week ago in class, the victim's mother said.

Sadie Baze said her daughter, Shana Fisher, 16, was gunned down during art class at Santa Fe High School on Friday.

Baze said the suspect had pestered her daughter to go out with him for months. A week ago, her daughter stood up in class and told Pagourtzis that she wouldn't go out with him.

Before asking Shana out, the suspect had previously dated her best friend, Baze said, adding that's why she told her daughter to turn him down.

"One of the shotgun shells was for my daughter," Baze said. "She's never going to walk through the front door again."

Shana had turned 16 days earlier.

'I was frozen'

Pagourtzis used a shotgun and a revolver to shoot students and teachers, killing 10 people, police said. An additional 13 others were injured.

Deedra Van Ness' daughter, Isabelle Laymance, survived the shooting by hiding in a classroom closet. In a Facebook post Saturday titled "longest day of my life," she said her daughter told her the gunman was "yelling Woo Hoo!" as he fired in the classroom next door.

When her daughter first called to let her know about the shooting, she was whispering to avoid alerting the gunman.

"I was frozen, standing there with no idea what to do next," Van Ness posted.

The mother said she texted their friends and relatives to ask them not to call Isabelle to avoid giving away her hiding place.

The victims

One of the students killed was Jared Black, who turned 17 last week and was supposed to have a birthday party Saturday.

Other victims included Sabika Sheikh, a Pakistani exchange student; Chris Stone, 17; Angelique Ramirez; Christian Riley Garcia; Aaron Kyle McLeod; Kimberly Vaughan; Glenda Ann Perkins and Cynthia Tisdale, who were teachers.

The people hospitalized included retired Houston police Officer John Barnes, who served as a resource officer at the school and confronted the gunman.

Houston Police Chief Art Acevedo tweeted Friday that he had visited Barnes in the hospital, and he was "hanging in there."

Suspect is 'confused'

JUST WATCHED Suspect posted image of 'Born to Kill' shirt Replay More Videos ... MUST WATCH Suspect posted image of 'Born to Kill' shirt 01:22

The alleged shooter used a shotgun and a .38 revolver legally owned by his father, Gov. Greg Abbott said.

The suspect's family issued a statement Saturday, saying they are shocked and confused, and expressing condolences to the victims. Pagourtzis is a "smart, quiet, sweet boy," they said.

"While we remain mostly in the dark about the specifics of yesterday's tragedy, what we have learned from media reports seems incompatible with the boy we love," they said.

The family said they are cooperating with investigators and will make no other public comments until the fact-finding stage is completed.

Pagourtzis is being held without bail and is accused of capital murder of multiple people and aggravated assault on a public servant. He has not entered a plea.

Attorneys Robert Barfield and Nicholas Poehl said they had met with Pagourtzis for two, 30-minute visits. Barfield said his client is "not doing well" and is "confused."

"I think that at this point, I think he's in some kind of shock," Poehl told CNN on Sunday. "It's going to be a while before I can tell you more."

The suspect won't face the death penalty if he is convicted. Under Texas law, offenders who are under age 18 and charged with a capital offense face a maximum punishment of life in prison with the possibility of parole after 40 years, according to Robert Dunham of the Death Penalty Information Center.

The suspect told an investigator he acted alone and spared people he liked because he wanted his story told, according to a probable cause affidavit.

Gunman acted alone

Gunfire started not long after classes began around 7:30 a.m. (8:30 a.m. ET), officials said.

Two school resource officers were on the campus and confronted the shooter, Abbott said.

Authorities later found explosive devices -- including pipe bombs and pressure cookers -- in and near the school, a law enforcement official said.

Galveston County Judge Mark Henry told reporters that the suspect had devices but none were functional. One was a pressure cooker with an alarm clock and nails, but no explosive material. Authorities also found an unlit Molotov cocktail, he said.

Investigators believe Pagourtzis acted alone, a law enforcement official told CNN on Saturday.

'We will grieve together'

This is the 22nd US school shooting so far this year, and the third instance in eight days in which a gunman was on a school campus.

President Donald Trump addressed the school shooting, saying that mass shootings have been "going on too long." He said federal authorities are coordinating with local officials.

The Santa Fe school district will close its schools Monday and Tuesday, officials said -- but students and staff are slowly being allowed to collect their belongings from part of the high school.

The community of Santa Fe is in mourning, its congressman said, and residents "will pull together" like they did after Hurricane Harvey months ago.

"We will grieve together, we will love one another, we will work together. We did it after Harvey -- still doing it after Harvey," US Rep. Randy Weber told reporters Saturday, referring to the storm that ravaged the Houston area in August . "We'll do it after this."

"We will get through this," he said.