University student Adam Ali, 18, had already been caught speeding on a motorway and improper use of his car horn despite passing his test just weeks earlier.
West Midlands Police arrested the youth, who cannot be named because of his age, on Tuesday, around four hours after Leo, aged 12, suffered fatal injuries on a riverside path.
A teenager being quizzed by police in connection with the murder of a 'kind' 12-year-old schoolboy has been further arrested over assaults on three pensioners aged in their 70s and 80s.