CBC has obtained dramatic footage showing New Brunswick teenager Ashley Smith, who died in prison in 2007, being pepper sprayed and about to be jolted with a Taser in her cell during the almost four-year period prior to her death.

The video, which will be broadcast Friday night on CBC's The Fifth Estate, was shot by prison staff in New Brunswick and provided to the program with guards' faces obscured and their voices altered.

Smith, who committed a series of minor offences, spent from 2003 to 2006 in two New Brunswick correctional facilities before ending up in a federal women's prison near Kitchener, Ont. She died of asphyxia with a ligature around her neck in her cell in October 2007 at the age of 19.

Her case prompted a probe by New Brunswick's ombudsman and federal correctional investigator Howard Sapers. It also drew widespread criticism about how young people suffering from mental illness or severe behavioural disorders are dealt with by the prison system.

A fellow prisoner in New Brunswick said Smith deliberately provoked guards and repeatedly pretended to choke or strangle herself by wrapping things around her neck. When guards responded, she refused to comply with their orders.

The video shows guards physically subduing her, spraying her with pepper spray and preparing to shock her with a stun gun.

"Ashley was Tasered twice in the space of one month," provincial ombudsman Bernard Richard told The Fifth Estate. "Repeatedly, that was the response to her behaviours.

"I think someone should have clued in that this girl required much more professional help," he said.

Richard said the youth centre superintendent decided to transfer Smith to a federal prison, partly because "without question, they were at wit's end," but also out of a belief it would be better for her.

"They, I think, really felt that she might be able to get more help in the federal system," he said.

After Smith was transferred to the federal prison system, she continued to defy guards and used broken glass to cut strips from her prison gown and tie them around her neck.

Jason Godin, Ontario president of the guards' union, said when guards would go to her aid, they were sometimes attacked.

Godin said guards were eventually told by their superiors not to enter her cell to remove ligatures from her neck.

"Our members were told not to enter Ashley Smith's cell until she stopped breathing," he said.

"There was daily direction given, right from the highest levels of management all the way to the front-line staff that 'You are not to go in the cell. This is your orders,'" he said.

Smith was seen with a ligature around her neck on Oct. 19, 2007, but guards delayed entering her cell until it was too late. She was pronounced dead at 8:10 a.m.