(CNN)Four weeks after alleged gang members lured 9-year-old Tyshawn Lee into an alley and killed him -- a slaying that some in violence-riddled Chicago called a new low -- the city's police superintendent announced the arrest of one man and vowed to "obliterate" the "criminal" group to which he belonged. "That gang just signed its own death warrant," Superintendent Garry McCarthy said Friday. "We're going to go in and destroy that gang and, by the way, the rival gang, too." McCarthy said Corey Morgan, a 27-year-old "documented gang member (and) convicted felon," is in custody on a first-degree murder charge. But police don't think Morgan was alone, saying he acted "in concert" with two others. McCarthy didn't name one, who is in custody on an unrelated charge; the other, Kevin Edwards, is at large. Kevin Edwards is wanted in connection with the murder of Tyshawn Lee. "Who drove the car, who was on the scene, who pulled the trigger is all being worked on to delineate it," the superintendent said. "But we do know that these were the individuals who were involved in this." Bond was denied Friday to Morgan, prosecutors said. Court papers provided by the prosecutor's office said that "Tyshawn's death is the result of a gang war" between two particular gangs that "came to a boil" after Morgan's brother, Tracy, was shot and killed in a car with their mother on October 13. The mother was shot and wounded, court papers said. "Shortly after the shooting (Corey Morgan) stated that since his brother was killed and his mama was shot he was going to kill grandmas, mamas, kids and all," according to court papers filed in prosecutors' request that Morgan be held without bail.