Shelby Sosa, 15, says a substitute teacher took a bullet for her during a school shooting at Santa Fe High on Friday

Last Friday, Santa Fe High School freshmen Shelby Sosa was in her first period gym class about ready to play basketball when the fire alarm sounded off.

Sosa thought it was a random fire drill, like she gone through countless times before, and exited the gym with her twin sister, Tabitha and friends to head outside the school building. Little did she know that within minutes of hearing that fire alarm her life was going to change forever.

A shaken 15-year-old Sosa tells DailyMail.com in an exclusive interview how her substitute teacher Ann Perkins saved her life by pushing her out of the way at the last second, taking a fatal bullet instead from the accused killer.

Dimitrios Pagourtzis, the suspected gunman, is a 17-year-old Junior at Santa Fe High School located 30 miles south of Houston and accused of killing 10 people and wounding 10 others in one of the nation’s deadliest attacks since the Parkland, FL school shooting last February.

Sosa said, ‘We were getting ready to play basketball in first period when the fire alarm went, Ms. Perkins was substituting that day so she was in the gym with us.’

Sosa (pictured with her father John, her twin Tabitha and mother Christina) had been getting ready for gym class when the fire alarm sounded and the class began to evacuate

As students began to move from their classrooms at Santa Fe High School (pictured), they suddenly heard three loud bangs and began to run for their lives

Sosa says she was at the exit when she felt someone push her out the door moments before hearing a gunshot, and when she turned around she saw her substitute teacher Ann Perkins (pictured) had been shot just inches away from her

Sosa says as soon as she heard the fire alarm she exited the gym with her classmates and Ms. Perkins and started to walk down the hallway to exit the school building. ‘At that time we all thought it was just another fire drill exercise', she said.

But about half-way down the hallway Sosa said they heard three loud booms that sounded like gunshots. That’s when they all started to panic. ‘Ms. Perkins yelled out to everyone, "run".’

Sosa and her friends started running down the hallway, her twin sister Tabitha and another friend were ahead of her. As soon as they reached the door to the outside of the building Sosa said she paused at the threshold of doorway to look around and see where her other friend was at.

Sosa said, ‘I stopped at the door for a split second and noticed my friend had made it out okay - that was when I felt a shove in my back. The shove pushed me out outside the doorway. At first I thought it was a random student being pushy. At the time I thought to myself, "like calm down".

Sosa says Ms Perkins saved her life, and that she would have been shot if it wasn't for the devoted teacher

The teenager's mother says Ms Perkins (pictured) made the ultimate sacrifice in laying down her life for the young girl and that 'thank you is nothing but a drop in the ocean to what I owe her'

10 people were killed on Friday during the shooting, and grieving families have been leaving flowers at the school (pictured)

Within seconds of being pushed out the doorway, Sosa said she hear a single gunshot go off, she glanced over her should and saw Ms. Perkins grabbing the sides of the door trying to stand up.

‘She was shot. She tried grabbing the doorway trying to keep standing, she stumbled out the door and fell to the ground.’

Sosa said she crawled for a few steps before she fell to the ground outside the door. Ms. Perkins who was dying still was thinking of the safety of her students, her last words were, ‘run.’

‘As soon as we were outside there were cops all over, they told us to run and escorted to a safe part of the high school away from the building. I looked back again and saw Ms. Perkins lying on the ground just outside the door, inside I could see a police officer in the kneeling position with his gun drawn and looked like he was firing his weapon.’

Sosa (pictured) said she would never be able to repay Ms Perkins for her selfless act, but would try to live on as a better version of herself who is more appreciative of what she has

When asked what would she like to say to Ms. Perkins' family, Sosa and her family sobbed uncontrollably for several minutes.

After regaining her composure, the teary-eyed teen said: ‘I’ll never forget her, she saved my life. If it wasn’t for Ms. Perkins I wouldn’t be here today'.

‘There really isn’t anything I can say to Ms. Perkins family but thank you. Words will never be able to describe the gratitude I have for Ms. Perkins. She took a bullet for me. I’ll never be able to thank her enough. Anything I say would pale in comparison for what she did for me.’

Christina Sosa, Shelby’s mother said, ‘As a mom I want to thank her, she saved my daughter’s life. It hurts to know that Ms. Perkins family had to lose her in the process. Our pastor told us there is no greater love than for someone to lay down their life for a friend and Ms. Perkins is a perfect example of this.

‘Ms. Perkins was a teacher who obviously went above and beyond by saving Shelby, a thank you is nothing but a drop in the ocean to what I owe her.

‘Now Shelby can go change lives like Ms. Perkins did.’

Ms. Perkins was beloved by her students. One wrote on Twitter: ‘Ann Perkins was a beloved teacher, family member, friend, and woman. She enjoyed spending time with her children, grandchildren, and students. She lived an impeccable life filled with traveling, love, family, & a bit of champagne. Rest easy our beautiful nurturing angel.’

Sosa said she had never met or heard of Dimitrios until last Friday. She said that she wouldn't have too many nice things to say to him if ever given the chance but wants to ask him, ‘why did he have to do that?’

Dimitrios Pagourtzis, the suspected gunman (pictured in old yearbook photos), is accused of killing 10 and injuring 10 when he opened fire at his high school in Santa Fe on Friday

Sosa said her perspective on life has changed since the school shooting. She said she was going to try not to be so selfish and be more appreciative of the things she has in her life.

Freshman Robert Montemayor led about 10 students out of the school to the safety of his home about a half mile away after he heard gunfire.

The 15-year old student said he was late for class last Friday and walking down a hallway when a fire alarm sounded. He had his earbuds in, but said he faintly heard the gunshots erupt. A male teacher come out into the hallway and told everyone to ‘run.’

After he left the school building not knowing if more gunfire was coming he took several of his friends from an area across the street from the high school to his house about a half mile away.

‘I went back and forth a couple of time bringing my friends to my house where I knew they would be safe until their parents came, said, Montemayor.

He hurt his hand in the melee crossing a fence but said he would do it all over again. ‘I didn’t know if there was going to be more shooting and wanted to get away from the school as soon as possible and knew my house was a safe place for my friends.’

Freshman Robert Montemayor (pictured) led about 10 students out of Santa Fe High School to the safety of his home about a half mile away after he heard gunfire on Friday

He injured his hand in the process (pictured) but continued to go back and forth, rounding up more students to help them get somewhere safe

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, Dimitrios Pagourtzis told investigators 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.

Texas Governor Greg Abbott called the shooting ‘one of the most heinous attacks we've ever seen in the history of Texas schools.’

Pagourtzis (pictured left in Year 8, 2015, and right in his mugshot) told investigators he did not shoot students he liked, because he wanted his story to be told

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 (pictured is the trailer owned by Pagourtzis' parents that the teenager spent multiple days a week at)

As of Saturday night, the FBI was still searching the trailer, where they allege he put together many of those explosive devices

Authorities searched two homes in nearby Alvin, Texas, one where he lived with his parents and another rental trailer home that has been empty for months.

A neighbor who lives next door to the Pagourtzis’s rental trailer home, Charity Killman, told DailyMail.com: ‘Dimitrios used to come by the rental trailer a few times a week. In the past couple of weeks he came by three to four times a week. The last time I saw him was the night before the shooting'.

'He never said anything to me, not even a "hello". When he came by he usually came by himself and spent about 20 minutes there. I never saw him wear a trench coat nor did I see him bring in anything or take anything out of the trailer.'

Dimitrios’ family has gone into hiding but DailyMail.com spoke with a few relatives.

‘I can’t talk about it. We don’t have any comment to make right now,’ Amanda Pagourtzis, a relative of the gunman, told DailyMail.com at her home in Pearland, Texas.

A man who came to the door at the house of his 74-year-old grandmother Margaret Kosmetatos in nearby League City said: ‘Keep your nose out of this. Get off our property.’

The FBI are still searching the family home as of Saturday night.

Charity Killman (pictured) lived next door to the Pagourtzis' trailer. She said she saw the teenager come and go multiple times a week

Ms Killman says she never saw the high schooler bring anything or take anything from the trailer

She says he was there the night before the shooting though (pictured is a window into the trailer)