A fourth man has been arrested in connection to the death of 18-year-old Lukas Strasser-Hird in a Beltline alley in late November.

He is facing a charge of second-degree murder. Three other suspects have already been arrested and charged.

Lukas Strasser-Hird died after suffering critical, life-threatening injuries in the alley located at Second Street and 10th Avenue S.W. An autopsy confirmed he died from stab wounds.

It's believed Strasser-Hird was involved in two altercations before his death. After the first incident, he and friends were separated from the situation but ran into another group of people shortly after. 

Police believe several people were involved in the incident, and the investigation is still underway.

Officials also made a public appeal for cellphone photos or video of a deadly assault. 

"Investigators believe that some onlookers may have used their cellphones to video or photograph either or both of the altercations," said police. "These images may have been shared and police are keen to obtain them as the investigation continues."

Videos or photos can be sent to a special email address that has been established for the investigation at homicidetips@calgarypolice.ca.