DETROIT —  A jury has convicted an 18-year-old man of killing another man, then beheading him and torching the body in what prosecutors called a thrill killing.

Jean Pierre Orlewicz of Plymouth, Mich., was charged with first-degree murder in the Nov. 7 slaying of Daniel Sorensen, 26, of River Rouge in Wayne County's Canton Township. The jury convicted Orlewicz on Wednesday, a day after starting deliberations.

The conviction carries a mandatory punishment of life in prison without parole.

The defense had argued in Wayne County Circuit Court that the Orlewicz killed the much larger Sorensen in self-defense and mutilated the body because he feared reprisal by organized crime figures.

But prosecutors say Orlewicz carefully planned the killing.

Orlewicz testified he stabbed Sorenson after the 280-pound bar bouncer pointed a gun at him and friend Alexander Letkemann.

Letkemann, 18, of Westland, Mich., testified against Orlewicz last week after pleading guilty to a reduced charge of second-degree murder.