COMMERCE CITY, Colo. -- A shooting that killed one teenager and wounded his brother has brought attention to two gangs that detectives hadn't focused on recently.

Now investigators are trying to determine whether the groups are minor players or a force that needs to be monitored.

"They took a big step into the big leagues," said Lt. Jim Welton, commander of the Metro Gang Task Force.

The shooting killed Bennie Williams, 15, and injured Rodney Williams, 16, at a park near Adams City High School on Thursday in an attack that witnesses said carried over from a fight the day before. Nearby schools were closed for the day after the shooting.

The brothers presented themselves as members of a gang that formed years ago on Denver's west side, The Denver Post reported.

Paul Pena, the 19-year-old held on suspicion of being the shooter, was a member of another gang, the newspaper reported. Two 15-year-olds identified as part of the same gang were being held on probation violations.

Jos Munoz, 20, was being held for investigation of being an accessory to the shootings.

On Saturday, police increased patrols to stem retaliation efforts and to remove inflammatory graffiti, colors or markings from a tree serving as a memorial to Bennie Williams.

Dozens of red rags were replaced by a sign that read: "The red rags are the reason he was killed. So you kids need to think on how you are letting him rest in peace."

It was signed, "Mr. Williams."

According to court documents, witnesses told police that Rodney Williams punched Pena's brother Wednesday in a fight that also may have involved Bennie Williams.

The next day Pena, Munoz and at least four juveniles were at a park when they saw the brothers, according to court documents. Pena, Munoz and the brothers began to scuffle. According to an arrest affidavit, Munoz knocked Bennie Williams down and beat him, as Rodney Williams stabbed Munoz with a screwdriver.

A parks worker told investigators that Rodney Williams was shot three times as he tried to run away, and Bennie Williams was shot from about 3 feet away as he tried to crawl away.