Shocking video shows moment before glamorous elementary school teacher, Elvia Espinoza, 46, was stabbed 70 times to death by her pre-med son, 21, because 'she got on his nerves'

Shocking doorstep video captures the terrifying moment before a beloved Florida elementary school teacher was killed by her pre-med student son.

Emmanuel Espinoza, 21, was seen hiding a knife behind his back as he attempted to open 46-year-old Elvia Espinoza's door on Saturday.

The student, dressed in light blue jeans and a navy-blue shirt, casually approached with one hand concealed behind his back.

'He knocked on the door, and his beautiful mother was so excited to see her son. She opened the door,' Polk County Sheriff Grady Judd said as he played the footage during a press briefing. 

Judd said Emmanuel charged in the house and started stabbing his mother the second the door was opened. 

A shocking doorstep video captures the terrifying moment before Elvia Espinoza, 46, a beloved Florida elementary school teacher, was allegedly killed by her pre-med student son

Elvia Espinoza, 46, a beloved Florida elementary school teacher, was allegedly stabbed to death by her pre-med student son

Emmanuel Espinoza (pictured), 21, allegedly stabbed his mother in excess of 70 times' without saying one word

Emmanuel told investigators that he knew where to stab his mother for maximum effect because of his biology classes, according to Sheriff Judd. 

He was traveling to attend a family event when his mother. Elvia asked if he would stay at her house for the weekend, according to authorities. 

He arrived at the second-grade teacher's house around 2 pm, and when she opened the door, he allegedly stabbed her 'in excess of 70 times' without saying one word as Elvia screamed for 'many, many, many times,' Judd said. 

The sheriff's office is holding off on releasing the audio from inside the house.  

'We talked to him and he confessed, he said 'you know I have wanted to kill my mother for many, many years because she got on my nerves,'' said Judd.

Investigators found that Emmanuel stabbed his mom more when she was trying to get up off the floor. 

He once again stabbed his mother more when he found Elvia's hands were still moving, Judd said. 

'As soon as he murdered her, he dialed 911 and immediately confessed to the 911 operators.' 

The sheriff said they asked Emmanuel about his relationship with his mother and he said that he really loved her, but she irritated him, so he decided to kill her. 

'He once again told us that he loved his mom,' Judd said during Monday's briefing. 

Polk County Sheriff Grady Judd said Emmanuel (second from the left) admitted to wanting to kill his mother (second from right) for years because 'she got on his nerves' 

Polk County Public Schools confirmed to DailyMail.com Elvia was a second grade teacher at Frostproof Ben Hill Griffin Jr. Elementary

Emmanuel reportedly told detectives in his confession that he had cut his hand on the knife while stabbing his mother. 

'And as he standing at the kitchen sink, washing himself off and the knife, he wanted to ask his mother for the Neosporin, for the cut on his hand. But he noticed she was dead,' the sheriff said. 

Judd said Emmanuel has been cooperating with investigators and is charged with first-degree murder.

'And as he standing at the kitchen sink, washing himself off and the knife, he wanted to ask his mother for the Neosporin, for the cut on his hand. But he noticed she was dead,' the sheriff said. 

Polk County Public Schools confirmed to DailyMail.com Elvia was a second-grade teacher at Frostproof Ben Hill Griffin Jr. Elementary.

'Her students and colleagues greatly loved her, and her sudden, unexpected death is a devastating loss. She was a very special part of her school family,' said the district.

The school made calls to the parents of all of her students and will have grief counselors available of the community Monday.

Tributes have been pouring in online for the beloved mother, teacher and community member.

The sheriff said they asked Emmanuel about his relationship with his mother and he said that he really loved her but she irritated him, so he decided to kill her

Tributes have been pouring in online for the beloved mother, teacher and community member

University of Florida pre-med student Emmanuel Espinoza (pictured) was driving from Gainesville to Frostproof when he decided to kill his mother

'Elvia always had a smile. Loved her family and her children. Was proud to be a teacher and worked hard to be one. She was one of my best students, a co-worker, and a fellow teacher, ' said Nancy Murray DeMarco.  

'Elvia Espinoza was the sweetest person to me and my family she was always cheerful and kind,' said Sherry Dacres.

'So many memories of chatting outside at the end of a long day. She truly loved teaching and was so proud of being a grandma. What a sad day in our little town, rest in heaven my dear friend.'

'Elvia there aren't adequate words to describe what we're feeling. You were such a kind, sincere, loving and caring person that, to know you're gone makes the world a little more dim,' said Monica Alvarado.

'I always admired how you poured your heart into everything and everyone around you. We are all devastated beyond belief. Thank you Elvia for loving us and being everyone's biggest cheerleader. I love you and you are missed beyond measure.'