SANTA FE, Texas -- Ten people were killed and 10 wounded in a shooting Friday morning at a high school south of Houston, authorities said. The shooting at Santa Fe High School was the nation's deadliest such attack since the massacre in Florida that gave rise to a campaign by teens for gun control.

Two substitute teachers and several students were killed in Friday's shooting. Another 10 people were wounded in the attack, Texas Gov. Greg Abbott said at an afternoon news conference.

Officials began identifying those killed in the attack Friday afternoon, including Ann Perkins, a substitute teacher at the school, and Sabika Sheikh, a Pakistani exchange student.

Get Breaking News Delivered to Your Inbox

"Our thoughts and prayers are with Sabika's family and friends," said Aizaz Ahmad Chaudhry, Pakistan's ambassador to the U.S.

Dimitrios Pagourtzis Galveston County Sheriff's Office

The suspect in custody was identified as 17-year-old Dimitrios Pagourtzis, Galveston County Sheriff Henry Trochesset said in a statement. He was being held without bond on a charge of capital murder. Harris County Sheriff Ed Gonzalez said the suspect was believed to be a student at the school.

Investigators said Pagourtzis admitted to authorities that he went on a shooting rampage at a Southeast Texas high school that left 10 dead, most of them students.

According to a probable cause affidavit, however, Dimitrios Pagourtzis told investigators that when he opened fire at Santa Fe High School on Friday morning, "he did not shoot students he did like so he could have his story told."

Pagourtzis is being held without bond at the Galveston County Jail. He is charged with capital murder of multiple persons and aggravated assault against a public servant.

Authorities said they discovered homemade explosive devices in the school and nearby, including pipe bombs, at least one Molotov cocktail and pressure-cooker bombs similar to those used in the Boston Marathon attack.

Abbott called the shooting "one of the most heinous attacks that we've ever seen in the history of Texas schools."

Houston police chief Art Acevedo said school resource officer John Barnes is "hanging in there" after being shot in the arm. Barnes was the first person to engage with the suspect, officials said.

Two people of interest were being interviewed by authorities, Abbott said. He didn't identify them.

Pagourtzis' social media pages showed multiple images of guns. He recently posted a photo wearing a T-shirt reading "Born to Kill" and there were also photos of a long dark jacket with Nazi symbols.

Abbott said the suspect had said that he wanted to commit suicide after the shooting. "He gave himself up and admitted at the time that he didn't have the courage to commit the suicide," he said.

There was an active search for explosives, a federal law enforcement source told CBS News justice and homeland security correspondent Jeff Pegues. Authorities were in the process of rendering them safe and asked the public to call 911 if they see anything suspicious.

Sources confirmed to Pegues that authorities were searching property related to the suspect.

The suspect had a shotgun and a .38-caliber revolver, Abbott said. The suspect's father owned the weapons legally, Abbott said, adding that he didn't know whether the father was aware his son had obtained the weapons.

Student Damon Rabon told CBSN that he looked out his classroom door with a substitute teacher after hearing several loud bangs and saw the gunman.

"Black trench coat, short kind of guy, had a sawed-off shotgun," Damon said.

The substitute teacher then pulled the fire alarm in the hopes of alerting students and faculty in other areas of the school and getting them to evacuate.

Tyler Turner, a senior at the school, told CBS affiliate KHOU-TV that his friend saw "some kid" with a gun. When teachers and students were outside after the fire alarm was pulled, shots were fired, Turner said.

"As soon as the alarms went off, everybody just started running outside," sophomore Dakota Shrader told reporters, "and next thing you know everybody looks, and you hear boom, boom, boom, and I just ran as fast as I could to the nearest floor so I could hide, and I called my mom."

Turner said he ran behind some trees, heard more shots, jumped a fence and ran to a car wash. He said he saw firefighters treat a girl who had a bandage around her knee and may have been shot.

Rome Shubert, a sophomore at the school, was treated for a gunshot wound to the head. "[The gunman] had fired 10 to 12 shots in the room before he left," he told CBS news. "I'm one of the lucky ones and I'm glad that God spared me but I just feel bad they didn't make it. They had no reason to be shot -- they didn't deserve that."

Students from the high school were transported to another location to reunite with their parents.

President Trump, who was in Washington, initially reacted to the shooting on Twitter.

School shooting in Texas. Early reports not looking good. God bless all! — Donald J. Trump (@realDonaldTrump) May 18, 2018

Later, while speaking at an event on prison reform, Mr. Trump said it was a "very sad day."

"This has been going on too long in our country," he said. "Too many years, too many decades now. We grieve for the terrible loss of life and send our support and love to everyone affected by this absolutely horrific attack. To the students, families, teachers and personnel at Santa Fe High, we're with you in this tragic hour, and we will be with you forever."

According to a law enforcement official, the FBI was offering assistance, CBS News senior investigative producer Pat Milton reports. The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives also said it was responding.

There was a large law enforcement response to the same school in February when it was placed on lockdown after students and teachers said they heard "popping sounds." Santa Fe police swept the campus but found no threat.

The shooting on Friday was all but certain to re-ignite the national debate over gun regulations, coming just three months after the Florida attack that killed 17 people at Marjory Stoneman Douglas High School. In 2018 alone, there have already been 16 school shootings -- the highest number at this point during any year since 1999.

"It's been happening everywhere. I've always kind of felt like that eventually it was going to happen here too," Santa Fe High School student Paige Curry told reporters. "I don't know. I wasn't surprised. I was just scared."

In the aftermath of the Parkland, Florida school shooting, survivors pulled all-nighters, petitioned city councils and state lawmakers, and organized protests in a grass-roots movement.

Within weeks, state lawmakers adopted changes, including new weapons restrictions. The move cemented the gun-friendly state's break with the National Rifle Association (NRA), who fought back with a lawsuit.

In late March, the Parkland teens spearheaded one of the largest student protest marches since Vietnam in Washington and inspired hundreds of other marches from California to Japan.

The calls for tighter gun controls that have swelled since February have barely registered in Texas -- at least to this point.

Texas has some of the most permissive gun laws in the U.S. and just hosted the NRA's annual conference earlier this month. In the run-up to March primaries, gun control was not a main issue with candidates of either party. Republicans did not soften their views on guns, and Democrats campaigned on a range of issues instead of zeroing in on gun violence.