As investigators search for answers in the deadly shooting at a California synagogue, police are looking into the suspect's possible link to a fire at a nearby mosque and taking extra steps to keep places of worship safe.

One person was killed and at least three others wounded in a shooting on Saturday at Congregation Chabad in Poway, about 22 miles north of San Diego, authorities said.

The San Diego Sheriff's Department said it assigned deputies to religious centers throughout the weekend. While security has been heightened, authorities said it is not indicative of a greater threat.

"We encourage our communities to continue with scheduled events and other activities as normal," the department said in a statement. "The suspect in the Poway incident today has been captured and we believe he acted alone."

The suspect in custody has been identified as John Earnest, a 19-year-old student at California State University San Marcos.

He was booked into San Diego Central Jail early Sunday on one count of first-degree murder and three counts of first-degree attempted murder, according to the San Diego Sheriff's Inmate Website.

Authorities are investigating whether he is connected to arson at a mosque in nearby Escondido last month, San Diego County Sheriff Bill Gore said.

The San Diego Sheriff's Department is executing search warrants at the home and car of the suspect as well as at the synagogue, according to a release from the agency.

What happened in the synagogue

Gore told reporters that the gunman was armed with an "AR-type assault weapon." A witness told CNN affiliate KGTV there were six or seven shots followed by screams and then another volley of shots. The witness said a wounded rabbi tried to calm the gunman and members of the congregation.

Authorities said an off-duty Border Patrol agent, who Gore thinks is a security guard, fired at the shooter as he was fleeing the scene. He didn't hit the suspect, but Gore said it appears he hit the suspect's car.

It is unclear why the suspect fled but it is possible his gun might have malfunctioned, the sheriff added.

The suspect fled the scene and called 911 to say he was involved and give his location, San Diego Police Chief David Nisleit said. A San Diego K-9 officer arrived and the shooter surrendered without incident, he said.

Gore said the suspect was being interviewed by detectives and the FBI.

An open letter may give insight

Gore did not comment on a motive, but authorities are aware of an open letter posted online purportedly by the suspect, Gore said in a news conference.

Detectives are "collecting digital evidence" and are in the process of reviewing the online content "to determine its validity and authenticity," the sheriff said.

CNN has read through an open letter posted to the anonymous message board 8chan before the shooting.

In the posting, someone identifying as Earnest references killing Jewish people without making actual reference to Poway, San Diego or the synagogue involved in the shooting. The letter writer talks about planning the attack and references other attacks on houses of worship, including the attack on the Tree of Life Synagogue in Pittsburgh and the Christchurch mosque shootings in New Zealand.

The writer also talks about his disdain for Jews and claims responsibility for a mosque fire in Escondido last month -- a week and a half after the attacks in Christchurch. Graffiti referencing the New Zealand mass shooting was discovered at the scene of that fire.

The open letter is structured in a similar fashion to the manifesto linked to Christchurch attack suspect Brenton Tarrant, replete with a question-and-answer section in which the writer refers to questions he comes up with about his character, political affiliation and motivation for carrying out the alleged shooting.

The victims

The Palomar Medical Center received four patients from the shooting, according to a trauma surgeon. One patient died at the hospital, Dr. Michael Katz said.

An employee of the synagogue identified the woman killed as Lori Kaye, 60.

"The other three victims are doing well with their injuries," Katz said.

A 34-year-old man and a girl had shrapnel injuries. The man was identified by congregation member Roneet Lev as Almog Peretz, who was visiting from Israel.

The girl was wounded in a leg and in the face, and was transferred to a children's hospital. Her father Israel Dahan said that her name is Noya and she is 9-years-old. Peretz is her uncle, Dahan said, and he was injured protecting her.

A 57-year-old rabbi who was shot suffered what looked like defensive wounds to both of his index fingers. He will likely lose his right index finger, the doctor said. He has been identified as Rabbi Yisroel Goldstein, according to Palomar Health Public Relations Manager Derryl Acosta.

Congregation member Minoo Anvari, who said her husband witnessed the shooting, said the rabbi called for unity and prayed for peace even after getting shot.

"Rabbi said, 'We are united,'" said Anvari, a refugee from Iran.

As the rabbi was rolled into surgery, Lev said he told her that Kaye was killed after stepping between him and the gunman.

"She didn't die a senseless death," Lev said of her friend. "She died advertising the problem we have with anti-Semitism and to bring good to this world because she is the best person I've ever known."

The shooting happened at 11:23 a.m. (2:23 p.m. ET). The synagogue's Facebook page said a Passover celebration was scheduled for 11 a.m.

Passover, one of the holiest Jewish celebrations of the year, ended Saturday.

'Yet another wake-up call'

President Donald Trump, speaking outside the White House on Saturday, told reporters that the shooting "looks like a hate crime."

Many groups condemned the attack.

"Moving forward this must serve as yet another wake-up call that antisemitism is a growing and deadly menace," the Holocaust Memorial Museum said in a statement. "All Americans must unequivocally condemn it and confront it in wherever it appears."

Jonathan Greenblatt, CEO of the Anti-Defamation League, urged all religions to stand together in solidarity.

"All of these attacks on these sacred spaces represent a violation of our values that we as Americans hold dear: Values of decency, tolerance and respect. Whether or not you go to a church or a synagogue or a mosque, it's standing together with your fellow Americans that matters most," he said.

Abbas Barzegar, director of research and advocacy for the Council on American-Islamic Relations, applauded religious leaders and urged them to do more.

"Faith leaders around the world are already doing a great job working together to overcome the shared challenge of extremism," Barzegar said.

"They simply need to tell their story more and better, and most importantly spread that message down to the local community level and challenge hate in their own ranks."