Prosecutors have declined to explain the decision against filing charges.
Benjamin Wayne Diaz, 19, was arrested in Bakersfield a week ago and was extradited to San Joaquin County Jail in French Camp on Wednesday.
Riggins was found beaten to death in his Carlton Way home Nov. 17. A robber stole collectible coins and a few antique guns kept by the 72-year-old retired railroad worker, police said.
The one-time suspect's fate is unclear. He remains in county jail, and a San Joaquin prosecutor said the DA’s office is under the impression that he's wanted on a $50,000 Stanislaus County warrant for reportedly trying to sell marijuana.
Tracy police spokesman Sgt. Tony Sheneman said Diaz will not be released "any time soon."
However, a check of records by Stanislaus County Sheriff's Office Capt. Tim David shows no such warrant, the captain said.
Diaz was arrested in mid-November by the Modesto Police Department on suspicion of trying to sell marijuana, a felony, David said.
A $50,000 homicide warrant from San Joaquin County in Diaz’s name is still in the system, David said, despite the fact that Diaz was taken into custody on that warrant two days ago.
Diaz was scheduled to appear in court Friday afternoon on what were expected to be charges of robbery and homicide before the revelation was made that no charges would be pursued by San Joaquin County prosecutors.
Riggins’ stepdaughter, Rhonda Rallios, could not be reached for comment.
Sheneman said the investigation into Riggins’ death is moving ahead.