INDIANAPOLIS (AP) — A judge on Wednesday entered a not guilty plea for a man accused of plotting to kill a key witness against him in a deadly house explosion in Indianapolis.

Mark Leonard, 44, is charged with conspiracy to commit murder for allegedly trying to arrange the death of a witness who told police Leonard confessed to the November explosion that killed two people. The conspiracy charge carries a penalty of 20 to 50 years in prison.

Leonard, his girlfriend, Monserrate Shirley, and his brother Bob Leonard are charged with murder and arson in the Nov. 10 blast. Teacher Jennifer Longworth and her husband, John, were killed in the explosion that also left 33 homes in the Richmond Hill subdivision so damaged that they had to be demolished.

Judge Sheila Carlisle set a possible jury trial date in the murder-for-hire case for June 3. Leonard's public defender, Deana Martin, said the trial likely would be delayed.

Leonard asked a fellow inmate at Marion County Jail if he could put him in touch with a hit man to kill the witness, according to a police affidavit filed last week. The inmate, who Leonard believed belonged to a motorcycle gang, indicated he could help, and they drew up a contract agreeing that Leonard would pay a $15,000 kill fee on his release, the affidavit said.

Leonard later spoke on the phone with someone he believed to be a hit man, the affidavit said. The man actually was a federal agent.

Investigators believe Leonard and the others orchestrated the fatal explosion by removing a gas fireplace valve and gas line regulator so that the house filled up with natural gas, then set a microwave to start on a timer, sparking the blast.

The witness told investigators that Leonard had told him about the explosion a week before it occurred and that Leonard was already shopping for the Ferrari he intended to buy with the insurance money, according to a probable cause affidavit related to the original charges.

Prosecutor Terry Curry said in February he would seek life without parole for Shirley and the Leonards because a jury was unlikely to choose the death penalty.