(CNN) Prosecutors in Illinois are challenging the sentence of former Chicago police officer Jason Van Dyke, who killed a black teenager in 2014, sparking protests, a federal civil rights investigation and the eventual ouster of the police superintendent.

A jury convicted Van Dyke last fall of second-degree murder and 16 counts of aggravated battery with a firearm. In January, Cook County Judge Vincent Gaughan sentenced him to six years and nine months in prison on the murder charge for killing Laquan McDonald. Van Dyke fired 16 shots in about 15 seconds.

The aggravated battery charges carried potentially more prison time. Each of the 16 counts would have carried a minimum sentence of six years in prison. When combined, Van Dyke could have faced up to 96 years in prison, a stiff penalty many protesters and activists were hoping for.

Illinois Attorney General Kwame Raoul and Kane County State's Attorney Joe McMahon, the special prosecutor who tried the case, filed a petition -- called a writ of mandamus -- in the Illinois Supreme Court asking the court to vacate Van Dyke's second-degree murder sentence, authorities said. The petition asked to instead impose a sentence on each of the 16 counts of aggravated battery with a firearm.

They are also asking the court to determine which of those aggravated battery convictions "involved 'severe bodily injury' warranting consecutive sentences."

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