The prosecution's key witness at the murder trial of three army reservists took the stand on Wednesday, saying she heard screaming and then saw a homeless man being beaten.

Valerie Valen, a self-described recovering drug addict, told the court she was walking in Toronto's Moss Park in the early morning hours of Aug. 31, 2005 when she heard the commotion.

She said during the attack, a man shouted "all these bums -- these f---ing druggies, hookers, addicts, bums, homeless derelicts."

Valen testified she shouted at the men to stop their attack, and then they attacked her.

"They were hitting and kicking -- football kicking -- this poor man at the head of the bench, the belly and bottom of the bench," Valen said.

The 44-year-old said when she intervened, the men ran after her, kicked her legs out from under her and beat her from head to toe.

Valen testified that at one point one of the accused shoved his dog tags in her face and screamed, 'Who do you think you are? All you crack heads, derelicts and bums don't belong here. This is our park. This gives us the right to do what we want. We can kill you.'"

Valen, who wept at times during her day-long testimony, said the beating only stopped when she ran out onto Queen Street and a taxi drove by.

The Crown alleges a homeless man, 59-year-old Paul Croutch, was sleeping on a bench in the park when he was attacked by the three reservists -- Brian Deganis, Jeffrey Hall and Mountaz Ibrahim.

Croutch died of his injuries in hospital. The accused, all in their 20s, are on trial for second-degree murder.

The former Queen's Own Rifles members are also charged with assault causing bodily harm for the alleged beating of Valen.

Deganis, Hall and Ibrahim were at the nearby armoury for an event on the night of the attack, court has heard.

Major Peter St. Denis testified on Tuesday that Deganis and Hall seemed intoxicated, and that he had heard Deganis cursing the homeless who frequent the park and threatening to "take them on."

The three accused have pleaded not guilty to all charges. The trial continues.

With a report from CTV Toronto's Janice Golding