A California man is charged with murder after killing his girlfriend with a homemade cannon.

Richard Dale Fox, 39, pleaded not guilty on Thursday to first-degree murder in the death of Jeanette Ogara, 38. He's also charged with the explosion of a destructive device and child endangerment. The couple's 4-year-old daughter was in the trailer at the time and is unharmed.

Fox, also known as Richard Gail Barrett, is being held on $3.5 million bail.  He faces life in prison without parole if convicted.

The five-minute 911 call has been obtained by ABC News affiliate KGTV.

"It was my fault, it was an accident, I didn't mean it," Fox said on the 911 call.  "I don't think she's breathing."

On the call Fox is crying and apologizing to Ogara, whom he called his wife.

"I don't think she's alive anymore," he told the dispatcher.

When Fox allegedly lit the cannon filled with explosives, shrapnel debris from the explosion flew through the trailer siding and hit Ogara in the chest.  Ogara was pronounced dead on the scene and Fox's right leg was treated for shrapnel wounds before he was brought to San Diego Central Jail.

A friend of the couple told KGTV the couple's daughter is with her grandparents.

Detectives searched the trailer for explosives, finding the device described as a "cannon" according to the San Diego County Sherriff's office.

The investigation is ongoing and authorities have not yet determined a motive.  Fox is due in court March 16.

This is not Fox's first run-in with the law.  He pled guilty in 2009 to a misdemeanor battery charge against Ogara in October 2006, according to UT San Diego.

For that charge, Fox had been ordered to participate in a 52-week domestic violence recovery program and was placed on probation for three years.  A judge had also issued a limited protective order, which expired along with his probation in the beginning of January.