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The gunman was identified as Dimitrios Pagourtzis, 17, a student at the school. When he finally surrendered, nine students and one teacher had been killed.
Pagourtzis used two weapons in the attack on the school, according to Texas Gov. Greg Abbott, a shot gun and a .38-revolver, which belonged to his father.
The governor also confirmed a Molotov cocktail and “various other types of explosive devices” were found at the school and two other locations.
Authorities were interviewing two other people in connection with the shooting, but it’s unclear what part, if any, they played in the massacre.
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Update May 20, 8:13 a.m. EST: The Galveston County Criminal District Attorney released the complete list of the people killed in the shooting, the Houston Chronicle reported. The teachers were identified as Glenda Perkins and Cynthia Tisdale, 64. The students included Shana Fisher, 16; Angelique Ramirez, 15; Christopher Jake Stone, 17; Jared Black, 17; Christian Riley Garcia, 15; Sabika Sheikh; Aaron Kyle McLeod, 15; and Kimberly Vaughan.
Update May 19, 2:47 p.m. EST: Santa Fe High School students are being allowed to return to campus to pick up their cars and belongings left behind after Friday's deadly shooting.
According to a post on the Santa Fe ISD Facebook page, students with cars are meeting officials at the junior high cafeteria between 12 p.m. and 4 p.m. CST.
The school district states that students will not be allowed to go directly to the high school.
Update May 19, 2:14 p.m. EST: A teen who was shot in the leg during Friday's shooting at Santa Fe High School in Texas is in good condition, according to a Twitter update from the University of Texas Medical Branch.
A woman in the intensive care unit (ICU) is in serious condition.
John Barnes, the student resource officer and former police officer, remains in critical condition.
Officials gathered Saturday afternoon at Santa Fe High School in an adjacent grassy lot.
According to KHOU, the Santa Fe Independent School District superintendent and Santa Fe mayor called for unity and peace.
Galveston County Judge Mark Henry said there were no new updates to the investigation, KHOU reports.
Update May 19, 11:40 a.m. ET: U.S. Secretary of State Mike Pompeo issued an official statement on the death of Sibika Sheikh, the Pakistani exchange student who was one of the victims of the Santa Fe High School shooting.
Update 10:30 p.m. ET: Three of the victims in the shooting massacre have now been identified, according to news reports. A substitute teacher, Ann Perkins, an exchange student, Sibika Sheikh and high school junior Chris Stone are among the victims killed in the rampage.
The FBI and ATF are still processing the scene in Santa Fe, using SWAT teams, bomb techs and K-9 teams to search for explosives investigators say the suspect planted around the school.
Update 7:20 p.m. ET: Santa Fe High School shooting suspect Dimitrios Pagourtzis made his first court appearance in court and was denied bond on capital murder and aggravated assault.
Update 6:15 p.m. ET: Police are searching homes and cars for more explosives related to the attack on the school, CNN reported.
Pagourtzis, who wanted to kill himself, but surrendered instead, according to authorities, allegedly built explosives and planned to use them in the attack.
Federal authorities in Texas, including the FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives, are teaming up and scouring the crime scene at the school and surrounding locations, according to the FBI in Houston.
“The FBI Houston and ATF Houston are combining resources to meticulously process the scene,” the FBI said in a tweet.
Update 5:15 p.m. ET: The suspect in the Santa Fe High School shooting, Dimitrios Pagourtzis, has been charged with capital murder in the deaths of 10 people at the school Friday morning and aggravated assault of a peace officer for the shooting injury of school resource officer John Barnes, the Santa Fe Independent School District has confirmed. Pagourtzis is jailed without bond in the Galveston County Jail.
Schools superintendent Leigh Wall called the rampage “a terrible tragedy.
"Words cannot express the sorrow in our hearts for those we have lost," Wall said in a statement posted on the district's website.
“Our campus remains an active crime scene with law enforcement personnel from throughout our region supporting Santa Fe ISD Police Chief, Walter Braun.”
Wall also pledged to keep the community informed on developments in the investigation.
Update 4:10 p.m. ET: The school resource officer, John Barnes, who was wounded in the shooting rampage at Santa Fe High School is in the operating room and is in critical condition, University of Texas Medical Branch officials said at an afternoon press conference.
Barnes was injured in the arm, according to Dr. David Marshall, shot in the elbow.
There are two other patients at the hospital, a middle aged woman and a young male, but both are still unidentified.
The female patient suffered a fractured leg bone and is now out of surgery.
The male suffered a gun shot to the leg and is listed in stable condition, Marshall said.
Seven other victims were transported to several other medical centers near Santa Fe.
Update 3:15 p.m. ET: Governor Greg Abbott said during a press conference that Pagourtzis used two weapons, both of which were legally owned by his father, a shot gun and a .38-revolver. There are two persons of interest, one who is currently being interviewed by law enforcement and a second who will be.
Abbott says he plans to take action because people need to “do more than just pray for the victims and families. It’s time in Texas that we begin to take action to make sure this tragedy is not repeated ever again.” Abbott vowed to begin roundtable discussions next week to work on solutions to prevent shootings in the future. He plans to speak with anyone with a vested interest in stopping gun violence -- parents, students, those who want to support second amendment rights, safety personnel. He wants to address mental health to help prevent gun violence. He also said that the state needs to make sure schools have resources and can identify those who could pose a risk of violence.
According to Abbott, Pagourtzis had journals on his computer that outlined the attack and that he planned on committing suicide after the shooting.
Abbott also spoke to parents across the country telling them to “hold your children close tonight and let them know how much you love them.”
UTMB confirms that John Barnes is the man who is in critical condition. He is a recently retired detective who started working for the Santa Fe ISD police.
Update 2:33 p.m. ET: Police are talking to Pagourtzis. CNN is reporting he was injured in today's shooting but did not say what injuries he suffered.
Update 2:17 p.m. ET: A second person is now in custody in connection with Friday's deadly shooting. Earlier police said that a second person had been detained.
Update 1:44 p.m. ET: Clear Lake Regional Medical Center officials said that eight patients were taken to their hospital and of the eight, six have been discharged. Of the remaining, one patient is listed in critical condition. The other is listed in fair condition, KHOU reported.
KHOU is also reporting that the adult male being treated at UTMB was retired police officer John Barnes.
Update 12:35 p.m. ET: Santa Fe Independent School District police administration chief Walter Braun said that the campus has been cleared of all students and staff. Braun said that at least six people, including a SFISD police officer, were transported to area hospitals with injuries.
Doctors clarified that the adult male who has in the operating room did not have a chest wound, but had an upper arm injury, near the chest. The middle age female has been transferred to the operating room for surgery on her leg wound. The teen, who is a 16-year-old male, is in the pediatric ward with a wound to the leg.
Update 12:18 p.m. ET: The Santa Fe school district has confirmed via a Twitter post that police have found possible explosive devices at the school and off campus.
President Trump spoke earlier about this latest shooting.
Update 12:04 p.m. ET: Doctors at UTMB said that the adult male who is undergoing surgery is a middle aged man who has chest injuries. He has been listed in critical condition. Doctors said they are unsure how many times he was shot. The male teen who was admitted to the hospital was shot and has a leg wound and is listed in good condition. The other patient, who was being treated in the emergency room, has a gunshot wound to the leg also and is listed in good condition.
Update 11:47 a.m. ET: In a news conference with Harris County Sheriff Ed Gonzales there are between eight and 10 fatalities, but media sources are reporting 9 deaths. The majority of those killed are students according to the sheriff but there were some adult staff fatalities.
Law enforcement is doing a systematic search of the building to make sure that there are no additional injured students or students still in hiding. Police are also looking for any potential devices that were left behind.
Gonzales said it is an active crime scene and a family reunification area that has been set up to get families and their children reunited.
As for the shooter, Gonzales did not have an age or identification but said that the shooter was a male student at the school. Another student, again no name or age was available, was detained.
Update 11:14 a.m. ET: The University of Texas Medical Branch officials held a news conference. During it they announced that three patients have been taken to UTMB -- two adults and one person under the age of 18. Officials with the hospital said that an adult male was taken to surgery. One adult was still being treated in the emergency room and person under the age of 18 has been admitted to the hospital.
Harris County Sheriff Ed Gonzalez says that one person is in custody, another is detained. A police officer was hurt and is being treated.
Update: 11:06 a.m. ET: There are now reports of a possible explosive being found near an area roadway and the potential that the gunman was not alone, KHOU reported.
President Donald Trump has reacted via Twitter about this latest deadly school shooting.
Update: 10:40 a.m. ET: Two sources familiar with the situation have told KHOU that there are multiple student fatalities and that an officer was wounded. KHOU reported that once source was a federal official, the other was a county official, both close to the situation. Federal officials told KHOU that the suspected gunman was a student.
The district has a dedicated police force, including resource officers, crossing guards and a dispatcher, according to the district website.
Update: 10:20 a.m. ET: The school has confirmed that there are injuries, but there is no information on the extent of those injuries.
Update: 10:01 a.m. ET: Dr. Cris Richardson, the assistant principal of Santa Fe High School, quickly briefed the media outside the school. She told reporters that the active shooter has been arrested and secured. She did not disclose the suspect's name. School officials are starting to reunite students with their parents.
The school district had only two weeks left in the school year. Richardson confirmed that the school has trained for the situation.
Richardson had no details on any injuries.
Update: 9:54 a.m. ET: University of Texas Medical Branch has told local news outlets that patients are on the way to the hospital. They have no number of patients or their injuries. A news brief from the hospital is expected in a few hours.
The Galveston County Sheriff's Office told KPRC that one person is in custody.
Update: 9:37 a.m. ET: Witnesses told KTRK that it happened in an art class at the school. Santa Fe Police, Galveston County Sheriff's Office and ATF agents are responding, KTRK reported.
Neighboring schools are also in what is called “protect mode” because of the shooting at Santa Fe High School.
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Update 9:23 a.m. ET: KHOU is reporting that some students were evacuated to a business down the street from the school complex. There are unconfirmed reports that police exchanged fire with the shooter and that there may be injuries, KHOU reported.
The school has also posted a warning to its website that reads:
The school also posted the message to its Facebook page.
The school usually starts its day at 7:10 a.m., according to the school website and dismisses at 2:35 p.m. On late-arrival days school starts at 9:15 a.m.
>>Read: Texas school marshals allowed to carry guns on campus
Original story: Details are still coming in, but it has been confirmed that police are on scene for an active shooter situation, KPRC reported.
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There have not been any official reports of injuries, KPRC reported.
However, a medical helicopter has been sent to the scene, KHOU reported.
The school district has confirmed that there was an active shooter situation at the high school.
A student at the school told KTRK that fire alarms went off around 7:45 a.m. local time and students left their classrooms. The student told the station that others thought they heard shots fired. She and other students, along with teachers, have found shelter near campus, KTRK reported.