An investigation is underway into the death of an Osceola man who was serving time in prison for a firearms charge.

Lonnie Painter was found unresponsive, with life threatening injuries, in his cell at a Chicago prison on Dec. 14.

Painter, 57, been sentenced to 15 years in prison after pleading guilty to being a felon in possession of a firearm. He admitted, last year, that he possessed two loaded 9 mm pistols that were purchased by his late wife.

The pistols were discovered when Painter’s vehicles were repossessed by a Michigan bail bondsman.

Painter was convicted previously of second degree murder in Tennessee and attempted murder in LaPorte.

Last year, the Bureau of Alcohol, Tobacco, Firearms and Explosives agents raided his South Bend home and business. Investigators also connected his name to remains of a woman found in Osceola.