The accused gunman who opened fire on a Taiwanese church in California lurked inside for hours — and even attended a lunch honoring a local pastor — before chaining the doors shut and carrying out the deadly shooting, the congregation said.

David Chou, 68, who lives in Las Vegas and spent some time in Taiwan in his youth, arrived at the Irvine Taiwanese Presbyterian Church in Laguna Woods around 10 a.m. before the Sunday morning service, according to a letter from the church obtained by the Los Angeles Times.

Chou — described as wearing a black shirt, which some witnesses said was emblazoned with the word “Security” — was greeted by a receptionist, who asked him in Taiwanese to fill out a form with his personal information, the letter said.

But Chou refused, telling her in Taiwanese that he had attended services at the church twice before and had already supplied his information.

Chou lurked around the church until the early afternoon, according to the letter, and then attended a lunch in honor of a pastor who had just returned from Taiwan.

After the meal, congregants spotted Chou “applying iron chains to start locking the doors shut,” according to the letter. When they confronted him about his actions, the 68-year-old reportedly refused to respond.

“They assumed he was a security guard,” the letter stated.

Chou was then allegedly observed using nails to hammer two other doors shut, the letter stated. Cops said the suspect also put superglue in the keyholes.

Chou, who cops say was armed with two legally purchased 9mm handguns, then allegedly fired one of them into the air, leading some witnesses to believe the sound was balloons popping.

The shooting killed Dr. John Cheng, 52, a sports medicine specialist from Laguna Niguel who tackled the gunman to try to stop the bloodshed, police and the church said.

“Chou shot Dr. Cheng dead with three bullets,” the letter from the congregation read. “Some church members then fell to the floor.”

Cheng’s actions allowed other congregants to pin down Chou and tie him up with extension cords, witnesses said. 

Sheriff Don Barnes called Cheng’s heroism “a meeting of good versus evil” that probably saved the lives “of upwards of dozens of people.”

Barnes said the motive for the shooting was Chou’s hatred toward Taiwan that was documented in handwritten notes that authorities found.

Chou’s family apparently was among many forcibly removed from mainland China to Taiwan sometime after 1948, Orange County District Attorney Todd Spitzer said.

Chou, who for years worked as a security guard, was booked on suspicion of murder and attempted murder and jailed on $1 million bail.

With Post wires