They were two veteran detectives who had done this countless times in their combined 38 years of police work. It should have been nothing more than a routine interview with a man suspected of misdemeanor sexual assault.

But the killings of Detective Sgt. Loran "Butch" Baker and Detective Elizabeth Butler on Tuesday afternoon, as they stood at the doorstep of a Santa Cruz bungalow, are a grim reminder that nothing ever really is "routine" in law enforcement.

"From every traffic stop to every knock on the door, you just never know what somebody is thinking," said Steve Belcher, a former Santa Cruz police chief. "You try to provide officers with the best guidance and the best training. But the reality is you can't be ready for every situation. If someone is absolutely determined to do you harm, you just can't prepare for that."

The slayings also were a sad echo of other recent Bay Area police tragedies where seemingly innocuous situations quickly spiraled out of control with horrific consequences.

California Highway Patrol Officer Kenyon Youngstrom, a 37-year-old father of four, was shot to death in September during a stop on Interstate 680 in Alamo. On March 21, 2009, one of the darkest days in California police history occurred when four Oakland officers were gunned down by a parolee -- a spree that also began when a vehicle was pulled over.

"Every time something like this happens, other officers think: 'There but for the grace

of God go I,' " said Chuck Wexler, executive director of the Washington, D.C.-based think tank Police Executive Research Forum. "It makes officers act with an even higher degree of caution. We want officers to be open, friendly and engaging. But tragedies like this give the public insight to why police sometimes act the way they do."

Baker and Butler had gone to question Jeremy Peter Goulet, 35, to get his side of the story about an incident where he broke into the home of a coffee shop co-worker and allegedly tried to assault her.

The detectives were unaware of Goulet's long history of run-ins with the law on sex-and-violence charges. Santa Cruz County Sheriff Phil Wowak added that there was no way for them to know Goulet, a former military police officer and Black Hawk helicopter pilot, held contempt for police and had told his father he would never go back to jail.

There was a conversation lasting about 10 minutes through Goulet's closed door when he refused to come out. Goulet then burst out through another door and shot the detectives with a .45-caliber handgun before they could react. Goulet was killed nearby in a wild gunbattle with other law enforcement officers.

"They were investigating a misdemeanor case," Wowak said. "Sgt. Baker has done this thousands of times. It's what we do every day."

That sentiment is keenly felt by police everywhere, and helps explain the outpouring of support for the traumatized Santa Cruz Police Department.

"Law enforcement as a profession understands that these things can happen anywhere, anytime," said Sgt. Jason Dwyer, a San Jose police spokesman.

The slayings in Santa Cruz rippled through the Oakland Police Department, which has lost 51 officers in the line of duty. Capt. Ersie Joyner said he has been having dreams and flashbacks this week to March 21, 2009, when a man wanted for violating his parole fatally shot two motorcycle officers who had stopped him on a city street and two more when a SWAT team entered an apartment where he was holed up.

"You never bounce back from something like that," Joyner said. "It changed my outlook every day when I leave my family knowing that I might never see them again."

Oakland's police chaplain, the Rev. Jayson Landeza, recalled spending the night of the shooting at a crowded police union headquarters trying to comfort officers. "You don't say anything in that situation," he said. "You just listen ... and you think of their kids and their spouses."

Landeza said there is still a "heavy-heartedness" within the department over the loss of Sgts. Mark Dunakin, Erv Romans, Daniel Sakai and Officer John Hege.

"I still get shivers when I talk about that day and that week," Landeza said. "The people of Santa Cruz will feel that way, too."

Dennis Kenney, a professor at New York's John Jay College of Criminal Justice who specializes in police issues, said law enforcement has been described as eight hours of boredom punctuated by two minutes of terror.

"And you just never know when those two minutes will come," Kenney said.

Much of the emphasis, he added, involves teaching officers to be on guard without appearing threatening. It is, he said, a balancing act.

"Effective policing comes when you're working with the community," Kenney said. "That doesn't happen when you're approaching people with your hand on a gun. But I think we owe it to them to give them a little bit of latitude when they sometimes act too forcefully."

There are indications that Butler, 38, and Baker, 51, were concerned as they went to Goulet's home. Neighborhood resident Jesse Lemic was walking past the house when the detectives sternly questioned him.

"They were very insistent that I identify myself and make sure that I was not involved in whatever was going on," Lemic said. "A few minutes later after I had walked home, I heard a volley of what obviously were gunshots."

For the first time in the nearly 150-year history of the Santa Cruz department, officers had been killed.

Nine cops have died in gun-related incidents this year across the country, according to the National Law Enforcement Officers Memorial Fund. Of those, six have been in California.

What makes the Santa Cruz incident all the more disturbing for those in law enforcement is these two officers were so experienced. Baker, a 28-year veteran nearing retirement, has been lauded for training much of the current Santa Cruz police staff.

"They were trained to be aware of their surroundings as much as humanely possible," said Belcher, who promoted Baker and hired Butler. "They did nothing out of the ordinary. But cops put their lives on the line every single day and every single night."

There is nothing routine about that.

Staff writer Matthew Artz contributed to this report. Contact Mark Emmons at 408-920-5745.