Four people who testified in cases relating to the San Mateo County District Attorney Office’s “Operation Sunny Day” case, under which 16 alleged members of three East Palo Alto gangs were arrested for a string of violent crimes, were arraigned this week on perjury charges, according to the district attorney’s office.

One of the four charged is an East Palo Alto resident and mother of defendant Miguel Rivera, who has been charged with the October 2012 murder of 21-year-old Christopher Baker in East Palo Alto. According to the district attorney’s office, Betty Jo Rivera, 52, provided a false alibi for her son to the police and then lied about the false alibi and alleged cover-up efforts to the grand jury. She was arraigned on Monday, Aug. 17, and her bail has been set at $500,000.

The district attorney’s office has also charged Joel Santana, 20, of East Palo Alto for stating during the grand jury proceedings that he did not know and had no contact with defendant Tyrone Love-Lopez. Love-Lopez has been charged with the killing of 21-year-old Lamont Coleman in East Palo Alto on Jan. 26, 2013. An investigation revealed cell-phone communication between the two men before and after Coleman was murdered. Santana also had Love-Lopez’s contact information in his cell phone, the district attorney said.

Santana pleaded not guilty and has a bail of $100,000.

Thirty-nine-year-old Germina Lapria Sturns of Hayward, the girlfriend of defendant Raymond Bradford, was arraigned Monday for allegedly lying several times during her grand jury testimony about her knowledge of Bradford and guns that he owned, the district attorney said. She also allegedly violated a court order not to discuss her testimony with anyone by visiting Bradford in jail in the days following and talking to him about it.

Sturns also pleaded not guilty. His bail was set at $125,000.

On Tuesday, 19-year-old Victor Manuel Galvez of Redwood City was arraigned after testifying at the grand jury proceedings that he was not a gang member and had no friendship with or knowledge of any of those convicted as part of the county’s “Operation Sunny Day” prosecution, according to the district attorney’s office. He also denied ever being on Sacramento Street in East Palo Alto — an area associated with the “Sac Street” gang. Police wire taps recorded Galvez talking on a cell phone to several “Sunny Day” gang members, and police also found photographs of him standing on Sacramento Street, according to the district attorney.

Galvez did not enter a plea Tuesday. His bail was set at $200,000.

All four charged with perjury remain in custody and will next appear in court on Aug. 26.

The grand jury investigation that resulted in the 16 arrests began in early January and took two months. The indictments were announced in late March. The alleged gang members are being blamed for a string of violent crimes that stretched from East Palo Alto to San Francisco, starting in September 2012 and continuing through December 2013.

Dubbed “Operation Sunny Day” after the code the persons arrested allegedly used to signify when a murder was successfully carried out, the 18-month-long investigation is the most massive case prosecuted by the San Mateo County District Attorney’s office in its history, District Attorney Steve Wagstaffe said at the time of the announcement.

Fourteen defendants appeared in court to enter their pleas in mid-June. Three of them — Roberto Gabriel Bustos-Montes, 24, of East Palo Alto; Emmanuel Imani Hyland, 25, also of East Palo Alto; and Palo Altan Nina Cragg, 24, — will not face the death penalty but could still receive life in prison without parole if convicted of the capital murder charges, Wagstaffe said in June.