49-year-old Martial arts instructor Kwang Kyung Yoo has been charged with murder in connection with the deaths of three people in Sydney.

The taekwondo teacher was known as Master Lion, and had taught the child in his studio, along with hundreds of other local children.

The body of Stephen Cho, 39, was found in a Baulkham Hills home at 10.30am yesterday after a concern for welfare report was made.

About two hours later, police found the bodies of Mr Cho’s wife, Min, 41, and a seven-year-old boy at the Lion’s Taekwondo martial arts studio in North Parramatta.

It will be alleged the woman and child had been strangled.

A friend of the family said the couple had been together for a long time before they got married, and were “very kind and humorous”.

She described the mother as a “sweetheart,” and said both parents adored their little boy.

About 11.50pm on Monday, Yoo arrived at Westmead Hospital with apparent slash wounds to his torso and arms.

He claimed he had been attacked at a carpark outside a Church Street supermarket in North Parramatta.

It’s now believed he allegedly sustained those injuries in an altercation with Mr Cho before he died.

Yoo has since undergone surgery at the hospital.

He was arrested at the hospital about 11.20pm yesterday and charged with three counts of murder about 9pm today.

CCTV footage has emerged showing Ms Cho’s BMW being driven, allegedly by Yoo, from the taekwondo centre to the home in Baulkham Hills.

Mr Cho was a senior estimator at construction firm Richard Crookes.

A spokesperson said the company was “shocked and saddened” by the “tragic passing of Steven Cho”.

Detective Superintendent Danny Doherty from NSW Police said the deaths were “cataclysmic” and “tragic”.

“We’re still establishing what other relationships there might have been,” he said on Wednesday.

“It was out of the blue, it was something that wasn’t forewarned, there was nothing that could’ve put a red flag up as far as we understand.”

He confirmed the slain boy had attended the martial arts studio as a student of the accused murderer.

Doherty said police would allege Yoo killed Ms Cho and the boy inside the studio on Monday and that at some point after 6.30pm that day, Yoo travelled to the Chos’ Baulkham Hills address where a confrontation with Mr Cho led to the third alleged murder.

Doherty said it was still very early in the investigation, but police did not believe anybody else was involved in the deaths.

Yoo’s neighbours said he was “nice to them” and they found the incident “shocking”.