Charles "Chase" Merritt was arrested in late 2013 in connection with the killings of Joseph and Summer McStay and their sons. (Photo credit: CBS)

SAN BENARDINO (CBSLA.com) — In less than a week, the man accused of killing the McStay family and burying their bodies in the high desert is set to begin his preliminary hearing after several major delays.

And now his attorney is speaking out and releasing new information in the case.

Charles “Chase” Merritt’s attorney Jimmy Mettias says the San Bernardino prosecutor’s office will say Merritt used a sledgehammer – found in the grave with the McStay family – to kill the McStays in their home and that he covered it up by returning to the house and painting over the evidence, CBS2/KCAL9’s Tom Wait reports.

Mettias says the prosecution will also try to use cell phone records to establish Merritt’s location around the time of the killings, according to Wait.

As for motive, Mettias told Wait the prosecution will argue Merritt was angry because McStay was going to cut ties with him after catching Merritt writing checks to himself from their business account.

Merritt and McStay worked in the fountain business together.

But Mettias told Wait the prosecution’s case will be light on evidence, claiming there is no physical evidence – DNA or fingerprints – to link Merritt to either the San Diego County home where the McStays were allegedly killed, or to the shallow grave in the high desert where the family’s remains were discovered.

The San Bernardino County District Attorney’s office says they have no comment on the newly released information.

When the McStays vanished in 2010, the San Diego County Sheriff’s Department initially treated their disappearance as a missing persons case.

Someone riding a motorcycle through a remote area of the high desert found the McStay’s remains in November of 2013. Merritt was arrested a year later.

In a jailhouse meeting with Merritt last month, Merritt told Wait that he is innocent of the charges.