A California man pleaded not guilty Friday to murder charges in the death of his girlfriend, whose skeletal remains were discovered in a jungle in Panama two years after she disappeared.

Brian Karl Brimager, 37, entered his plea after he was indicted by a federal grand jury in San Diego, the U.S. Attorney's office said.

Brimager has been in custody since June 2013 on charges including obstruction of justice and falsifying records related to the investigation into the killing of Yvonne Lee Baldelli.

The 42-year-old woman from Laguna Niguel, California, was last seen in 2011 when she arrived in Panama with Brimager.

The indictment alleges that Brimager murdered Baldelli, dismembered her body and disposed of her body parts in a remote jungle area. Brimager then engaged in an elaborate scheme to cover up the crime, including destroying evidence and sending a series of emails purportedly from Baldelli in order to make it appear to her friends and family that she was still alive, according to court papers.

The indictment also alleges that Brimager attempted to conceal his crime by disposing of a bloody mattress involved in Badelli's murder in the ocean. Brimager conducted two Internet searches on Baldelli's computer, one for "washing mattress" and a second for "washing mattress blood stain," according to documents.

A man who was cutting bushes on the island province of Bocas del Toro found a bag containing Baldelli's remains in August 2013.