Gentz, 49, of St. Clair Shores, Mich., was sentenced Tuesday to 17-28 years in prison after being convicted of second-degree murder for strangling Jane Bashara in January 2012, The Detroit News said.
After the sentencing, the prosecutor's office said the investigation into the homicide is ongoing.
Gentz pleaded guilty in December and said Robert Bashara bribed him to kill his wife by threatening him.
Robert Bashara, 55, was sentenced to 6-20 years in prison for trying to hire a Detroit furniture store owner to kill Gentz in jail but Bashara hasn't been charged in the death of his wife, the News said.
Jane Bashara's family, including her sister, Julie Engelbrecht Rowe, said her family doesn't believe the case is over.
"Mr. Gentz had no motive to murder our sister Jane," she told the Detroit Free Press. "We believe his statement that he was coerced into murdering her."
Gentz, who is developmentally delayed, asked for forgiveness Tuesday and apologized for his actions, the Free Press said.