The teen, named by family members as Joshua Smith, from east Detroit, allegedly unleashed a hail of bullets on Tamiko Robinson, 36, in the early hours of Monday morning, according to a police spokesman.
Smith, who was on the swimming team at Kettering High School, was said to be angry that his mother had tried to keep him off the streets and away from a gang.
Smith's uncle LeShaun Roberts, told Fox Detroit News the teen had wanted to 'hang with the big boys' - gang members in their twenties - but when his mother said no he ran away to relatives.
But Robinson, a dialysis patient, who was battling lupus, went after her son and insisted he came home, angering the youngster.
'He broke into his step dad's room, got a twelve gauge and brutally murdered my sister,' Roberts said. 'He shot at least ten times.
'He just shot. Every chance he got a chance to shoot again, he shot again, and there's just buckshot, holes everywhere.'
The little girl later asked relatives: 'why would someone want to hurt mommy?'
Smith was arrested soon after the shooting. He had reportedly been driving around in his mother's car.
Roberts, who was holding a framed portrait of the family, added: 'He (Smith) said his mother won't let him have friends, he said his mother won't let him bring his girlfriends over, his mother won't let him stay out until 11 o'clock at night. He's 14 years old.'
Detroit Police Chief Ralph L Godbee Jr and Mayor Dave Bing held a press conference yesterday to address Robinson's shooting and others involving children, including the shooting of a six-year-old boy in an attempted carjacking also on Monday.
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