A Calgary teenager accused of second-degree murder in the death a homeless man last year testified his own defence Tuesday, saying he kicked but didn't stab 45-year-old Gabriel Okeynan.

The accused was 16-years-old when he and a 13-year-old were arrested in connection with the death of Okeynan, who was found suffering from stab wounds in a smoking shelter near Marlborough Mall and died in hospital days later.

The younger of the pair pleaded guilty to manslaughter to last week.

Wearing a black hoodie, blue jeans and white running shoes, the older accused — who is now 17 — told a Calgary courtroom he met Okeynan at the Marlborough LRT station in June 2014 and it was Okeynan who asked if he and his young acquaintance wanted to go drink some beer.

He testified that the three then walked to an area near the mall, where he says Okeynan fell down.

He admitted he kicked the victim twice "gently" in the shoulder but said he never stabbed Okeynan or struck him with a weapon.

The accused can't be named under the Youth Criminal Justice Act.

During his testimony, he was frequently stuttering, repeating words and phrases, and appeared to have difficulty understanding his lawyer's questions.

Court heard he has a severe cognitive disability and an IQ of 45.

Justice Scott Brooker asked the accused why he kicked Okeynan.

"Why? Why? I don't know why," the teen replied. "I don't know why. I kick him cuz. Just cuz. It's like, I don't know why. I don't know why I kick him. I don't kick him too hard. Kinda tough questions for me. I can't explain it."

The 17-year-old was the only witness for the defence. Closing statements are set to be heard Wednesday morning.

The co-accused who pleaded guilty is set to be sentenced next month.