Napa police officers say they believe the suspicious packages that set off alarms Wednesday night were part of a prank targeting the family of controversial BART Police officer Johannes Mehserle.

The bomb scare lasted several hours before local law enforcement officers detonated two packages left at the east Napa home of Mehserle’s parents. Police evacuated residents from the area and kept others from their homes while inspecting, X-raying and eventually destroying the boxes.

Mehserle, 27, has been charged with murder in the shooting of Oscar Grant, 22, of Hayward at the Fruitvale BART station early New Year’s Day. Grant, along with several other riders, was ordered off a BART train after it was stopped because of a brawl.

Grant, who is black, was lying face down on the ground, while Mehserle, who is white, was trying to handcuff him. Officials say Mehserle pulled his handgun and shot Grant in the back. Grant was unarmed.

Grant’s death has aggravated racial tensions in the Bay Area and the demand that Mehserle be held accountable for his actions. Mehserle resigned from the BART police shortly after the shooting. On Tuesday, Mehserle was arrested in Nevada and charged with murder. He has been returned to Alameda County and is being held in the county jail.

Since the shooting, Mehserle and his family have been the targets of numerous death threats.

At about 4:30 on Wednesday, Mehserle’s parents found two packages — one medium-sized and the other smaller — at their Napa residence.

Because of the threats related to the high-profile shooting, authorities were called to the residence. The  Register is withholding details about the location of the residence to protect the family.

“We complied information about the delivery circumstances, and it caused us a lot of concern,” said Napa County Sheriff’s Capt. John Robertson.

Police closed down the area near the Mehserle’s home, and called in the county bomb squad to inspect the packages. The packages were X-rayed, and just before 9 p.m. they were destroyed and found not contain any explosive or hazardous materials.

“The investigation is ongoing, and because of the sensitivity of this case, we are not commenting on the contents of the packages,” Napa Police Cmdr. Andy Lewis said on Thursday. “We are releasing very little information about the investigation.”

Robertson said the department’s robot was used to view the packages on site Wednesday night. Once police figured they wouldn’t be able to determine what was in the packages, they were destroyed.

About 50 neighbors were evacuated from their homes. The evacuation started around 6 p.m., and residents were allowed to return to their homes about 9 p.m.