Police are seeking two persons of interest following the death of a Toronto man who was shot and killed while celebrating his birthday. 

Gaethan Kitadi was celebrating his 20th birthday over the weekend with friends in the east-end building where he lived with his family. 

He was escorting an uninvited guest out of the building when an argument started in the lobby, say investigators. 

Police had to fight through a large crowd of party-goers to get to Kitadi, who collapsed close to the spot where he was shot. He was pronounced dead at the scene.

Several witnesses did not stay to speak with investigators, said Det. Sgt. Justin Vander Heyden.

"The situation was chaotic, to say the least," Vander Heyden said. "But there is a murderer out there. We need to find him and these people, I guarantee, have the answers to my questions."

The persons of interest are both described as black males in their late teens to early 20s. One was wearing a white, hooded sweatshirt, the other was in a black puffy jacket with a blue, hooded sweatshirt underneath. 

The shooting happened at the building located at 11 Main St., near Kingston Road. The victim lived there with his family, though he was celebrating his birthday at a friend’s apartment.

Det. Sgt. Justin Vander Heyden talks about Gaethan Kitadi homicide

Toronto police Det. Sgt. Justin Vander Heyden told reporters Sunday that Gaethan Kitadi was not known to police. (CBC)

Vander Heyden said the party had been promoted on social media, though the people who organized the event were very careful about who was admitted to the building.

Police say a group of people arrived at the building shortly after midnight. Vander Heyden said that about 15 minutes later, a lot of people from the party moved to the lobby and vestibule of 11 Main St.

"What is obvious is that there is some kind of conflict between Mr. Kitadi, his friends and another group of people," Vander Heyden said.

He said "a great deal of the conflict" was captured on surveillance cameras at the building.

Though it is believed Kitadi was shot in the back, Vander Heyden said that must be confirmed in a post-mortem.

"It looks as though Mr. Kitadi turned to leave — I’m not sure if he saw a gun and attempted to flee, but he was shot in the upper body," he said.

So far, police have recovered physical evidence from the crime scene, though Vander Heyden said a weapon has not been found.

Vander Heyden said Kitadi had "no contact with Toronto police" prior to his death.

"Mr. Kitadi clearly didn’t lead a lifestyle that would lead him into this," he said. "It looked like he was trying to eject people from his own building, which was well within his rights."

Police ask the people present at the party to make contact with investigators.

"We’ve had some co-operation from other people in the party who allowed us to have access to their photographs that they took that night, and I have in excess of 100 different photographs of people who were at the party," said Vander Heyden.

"Unfortunately, I’ve only had a very small number of people come forward and speak to us about what had happened."

The slain man’s cousin, Christian Kitadi, said that Gaethan’s surviving parents and sisters are simply trying to "hold up" after receiving the devastating news about their son and brother.

"I don't know what happened he was a good kid, it was his birthday and he was having a party," he said Sunday.

His cousin was a talented basketball player, who was a top player on his high-school team.

"Basketball was his love," Christian Kitadi said.

With a report from the CBC's Natalie Kalata