Florida teen, 19, guns down his father and then executes his mother in front of cops responding to her desperate 911 call

A 'monster' teenager shot down his father and then executed his mother at point-blank range in front of cops before dying in a police shootout.

Police say they received a call just after 11pm on Saturday from a woman - later identified as Rebecca Ann Themelis, 48 - informing them that her husband, Christos Byron Themelis, 51, had been shot.

More gunshots could be heard while she was on the phone with the dispatch center, the Hillsborough County Sheriff's Office reports.

By the time deputies arrived at the home on Cactus Wren Place in Tampa, Florida, they found the suspect - Christos Alexander Themelis, 19 - and his mother, Rebecca, outside.

As deputies watched in horror, the suspect shot his mother in the back of the head and began shooting at the officers, injuring one deputy, the sheriff's office said. 

Dramatic body camera footage caught the stand-off between Christos Alexander and the deputies, beginning when they arrived on the scene and found him outside with his mother.

'Show me your hands, show me your f****** hands,' Deputy Shane McGough, 26, could be heard yelling.

He then pleaded with Rebecca to 'get out of the house now' and walk towards him, holding his gun drawn before radioing in, 'he's got her at gunpoint.'

'Listen, we don't want to hurt you, just let your mom walk to us, let her walk to us OK?' McGough tells the suspect, repeating his instructions to 'keep your hands up' and 'do not reach behind your back.'

As the son apparently retreats to go and grab his gun, McGough once again pleads with the mother to 'walk to me, walk into my flashlight.'

Then when Christos Alexander comes back out with the gun, he pleads, 'Ma'am get away from him now and come here.' 

Seconds after begging the suspect to 'stop reaching into your waistband', gunshots can be heard in the bodycam footage as both sides exchanges fire. 

McGough was struck in the leg, yelling 'I've been hit' at his fellow officers and asking for a tourniquet.  

Five deputies returned fire, causing the suspect to retreat into his home, the sheriff's office said in a press release.

At that point, authorities deployed a SWAT team, and deputies used a robot to enter the home through the front door.

'Unfortunately the first person we encounter on the ground is the father,' Sheriff Chad Chronister said at a news conference.

'The father had succumbed to his injuries.'

Police then found the suspect dead from injuries he sustained from the shootout in another room of the house.

But the situation could have been much worse, Sheriff Chad Chronister suggested.

'The monster we encountered this evening is responsible for not only injuring our deputy but also killing his own mother and father,' he said in a statement.

'Our deputies responded to a chaotic scene and immediately put themselves in harm's way to protect our community.

'Without our deputies' quick and skillful response, an entire neighborhood would have been in danger.'

None of the deputies involved in the shootout had any prior record of use of force, the sheriff's office added.

Deputy McGough is now in stable condition, and had surgery on Sunday to remove the bullet and insert a rod into his leg to help regrow the tibia - which was fractured in the shootout.

Authorities said the incident wasn't the first-time police have been called to the Tampa home.

Deputies have responded to incidents at the home 10 times prior, with the majority being related to mental health services and violence against the suspect's parents, Chronister said at the news conference.

He noted that there was also an active risk protection order against the 19-year-old that led deputies to seize his guns.

Investigators are now working to determine how Christos Alexander may have obtained the gun if he was deemed 'mentally unfit.'

'We don't know exactly and we may not ever know why he became as violent as he did,' Chronister said.

'But we do know inflicting injury or harm on another human being - it never matters what the reason is - it's never OK. Period.'