Portland police say the suspect accused of killing a man in the Parkside neighborhood last year had bullets in his apartment that appeared to match a shell casing found at the scene.

Tristin Chamberlain, 21, pleaded not guilty to murder during his arraignment Thursday afternoon. Prosecutors say Chamberlain shot 26-year-old Tyler Flexon of Portland on Nov. 29 after a fight inside the Mellen Street Market.

Chamberlain turned himself in to the York County Sheriff’s Office in December, less than two weeks later.

An affidavit from Portland Police Detective Daniel Townsend pieces together surveillance video and several witnesses who told police they saw two men fighting and heard a single gunshot outside the market where Chamberlain’s girlfriend was working that evening.

Video inside the market shows Flexon, Chamberlain and Chamberlain’s girlfriend in a serious argument about 90 minutes earlier.

Chamberlain is only in the video briefly but can be seen holding what police said appeared to be a gun.

Flexon stayed in the market for a while after Chamberlain left, spending much of the time shouting and looking at a window. Chamberlain’s girlfriend is seen shaking her hands in Flexon’s direction and the direction of the window. At one point, Townsend wrote, it appeared she was mouthing the words “go home.”

Several neighbors and witnesses described the shooter as a young, skinny man wearing all black under a royal blue puffy jacket, and slide-on shoes.

One witness was drinking beers on his porch along Sherman Street when he saw “two white guys who were calling each other the ‘n word,’ ” according to the affidavit. He said one man shot the other in the stomach and then ran down Mellen Street toward Park Avenue.

Another witness was making dinner in his girlfriend’s kitchen on Sherman Street, where he could see the Mellen Street Market through the window. He told police he could hear a man yell “Let’s do this, come out here” about eight times as a man wearing a royal blue jacket banged on the market windows.

At some point, the witness said, the man shouted something to the effect of “I’m going to shoot you,” before a second man could be heard shouting “Come and get me.”

A third witness was shopping at the market during the fight and saw Flexon run out the door, and later found him on the street, “gasping for air.” He told police that he recognized Flexon because he had seen him around the neighborhood before.

One witness who lives in an apartment building on Grant Street told police he heard gunshots, then saw a man run past his window into the back of the complex. The witness said the man had moved into the building three months earlier, but he didn’t know him. He later saw the suspect leave a key under the doormat. But the neighbor was unable to point Chamberlain’s photo out of a lineup with police later.

Officers got a search warrant for the Grant Street apartment and found several of Chamberlain’s personal items – including his driver’s license and debit card – as well as bullets in an extended-round Glock magazine left on a TV stand that had the same stamp as a shell casing found where the shooting occurred. Police also found a Cabela’s receipt listing the magazine purchased with a card that matched the last four digits of Chamberlain’s debit card.

Flexon came to Maine from the Poconos in Pennsylvania, according to an obituary from his family. He liked fishing and being out on the water.

“Our dear Tyler had many struggles in life, but lived his life to the fullest,” the obituary stated. “He made friends everywhere he went and he had a work ethic that was beyond compare. Tyler loved his family and would do anything for his friends and family.”

During his brief arraignment Thursday afternoon – the courtroom was mostly empty, except for Chamberlain’s defense attorney, Amy Fairfield, and prosecutors from the Maine Attorney General’s Office – Chamberlain entered a not-guilty plea. Cumberland County Superior Justice Thomas McKeon ordered that he will continue to be held without bail.