A Montbello teenager who was gunned down while walking to a bus stop in Park Hill on Sunday night was killed because he had blue on his shirt – the victim of a random gang shooting, his family said Monday.

Seventeen-year-old Marcus Mason was walking with his girlfriend when he was shot several times in the back of the head by killers he didn’t know. No words or dirty looks were exchanged, and Mason was not involved in gangs, his mother Josephine Baez said.

In fact, Mason, a senior at the Contemporary Learning Academy, was in the neighborhood to speak to a manager at a fast-food restaurant about a job, she said.

“He had on a blue, black and white striped shirt and we believe that’s why he was killed,” Baez, 40, said from her home, surrounded by grieving family and friends.

“His girlfriend said they walked by two boys and one of them just turned around and shot Marcus in the back of the head three times. It was a cowardly move.”

No arrests had been made on Monday, and detectives were still determining whether the shooting was gang-related, Denver police spokesman John White said.

Police did not identify Mason as the victim of the homicide, but his family did, and a makeshift memorial of stuffed animals and a poster reading “R.I.P. Marcus Mason” was set up at the intersection, one block south of Martin Luther King Park.

Across the street was a Crime Stoppers poster asking anyone with information to call anonymously 720-913-7867.

Neighborhood resident Marbella Bustos, 23, witnessed the shooting and asserted that no words were exchanged and that it appeared to be random violence.

“No one argued, no one said nothing,” Bustos said. “I just saw one of the guys shoot that boy, and then he didn’t run or anything. He just stood there for like 15 seconds over the boy and pointing his gun down at him and saying something. Then he walked off down 36th.”

Baez and her husband, Carlos Mason, were at the jazz concert in City Park when she spoke to her son by cellphone just minutes before he was murdered.

“That neighborhood is just out of control,” Baez said. “You can’t even have blue on your shirt, you can’t even ride a bicycle that’s blue; you have to spray paint it or it could get you killed.”

Marcus Mason dreamed of being a music producer and planned on entering his school’s music program. He also played football and basketball.

He was chubby most of his life. As an infant, he fell out of a window, and doctors told his family the only reason he survived was because he was such a fat little boy.

But within the past year he began to mature, his frame stretched and he stood 6 feet 2 inches – tall like his dad.

“I would have liked to spend more time with my son and helped him follow his dreams,” Carlos Mason, 39, said. “This is just senseless, senseless.”

His cherubic cheeks and smile lit up a room, family friend Renee Del Castillo said.

“He encouraged other kids younger than him to work hard in school, and he even made time to play with my 9-year-old,” Del Castillo said. “The world lost a really good heart in that kid.”

Staff writer Manny Gonzales can be reached at 303-954-1537 or mgonzales@denverpost.com.

To help out

Funeral arrangements for Marcus Mason are pending. A fund is being set up in his name at Horizon Bank outlets to assist his family.