SAN MATEO — Two communities and police departments are “dumbfounded” by the news that a former San Mateo police officer has been charged with a spate of rapes and sexual assaults while on duty, with a 17-year-old girl among the alleged victims.

Noah White Winchester, 31, was arrested Thursday morning near his Stockton home and was charged with 22 felony sexual assault charges that cover kidnapping with intent to commit rape, rape, sexual penetration and oral copulation under color of authority, sexual battery, criminal threats and forcible sex.

The charges against Winchester cover a two-year period when he worked in San Mateo and the Los Rios Community College District in the Sacramento area. He is in custody in the San Joaquin County jail on $3.1 million bail and is expected to be transported to San Mateo County by the end of the week to face the charges against him.

Prosecutors have tied Winchester to five victims and contend the sexual assaults occurred between July 2, 2013, and Oct. 19, 2015 across two jurisdictions where he worked as a police officer.

“It really is alarming and disturbing,” said District Attorney Steve Wagstaffe. “We’ve prosecuted officers for things on duty, but not for crimes as violent as these are. It’s truly a betrayal of the public trust and all of us in the criminal justice system are horrified by this.”

San Mateo police Chief Susan Manheimer said she was “appalled” at the nature of his alleged acts while acknowledging the former officer’s presumption of innocence in court.

“We are distressed, disgusted and disappointed by these allegations,” she said in an interview Thursday. “I am grateful to the victims who were courageous enough to come forward, and should the allegations prove true, we stand with them.”

She added: “We are taking all steps possible to ensure we do not get surprised and our community does not get targeted again.”

Winchester did not arouse suspicion until Oct. 20, when a woman told Burlingame police she was sexually assaulted in her car the previous night by a San Mateo officer, later identified as Winchester, at Coyote Point Recreation Area.

That led to both an administrative review and a criminal investigation by the District Attorney’s Office that culminated in Thursday’s arrest. It was during that investigation that authorities discovered allegations from 2013 while Winchester was a police officer with the Los Rios district.

The revelation has prompted an investigation by the college district, where Winchester worked from 2009 until 2015. He patrolled American River College in his last two years with the district, which covers the time frame of the allegations there.

“If these allegations are proven to be true, that would be horrific for the women who were victimized. Such criminal behavior is contrary to the core values and mission of the Los Rios Community College District,” district spokesman Mitchel Benson said.

Winchester was linked to two other assaults in San Mateo and two more around Sacramento. All of the victims were female, and all but one were adults, prosecutors say:

Oct. 20: Two counts of rape and one count of kidnapping in the Coyote Point case

Sept. 22: One count of residential burglary and one count attempted rape for an encounter in a San Mateo motel room

Sept. 15: Two counts sexual battery involving a victim at Hillsdale Mall in San Mateo

Aug. 30, 2013: Two counts digital penetration, four counts sexual battery and one count kidnapping involving a 17-year-old girl in a Los Rios Community College parking lot