LAS VEGAS — In the seven months since Heriberto Diaz Marcial was shot and killed walking home from his job as a casino porter on the Vegas Strip, church volunteers have knocked on hundreds of doors in his neighborhood and handed out fliers seeking information. The police released blurry security footage of a gray sedan tied to his three killers. His wife, Maria Diaz, has gone on television to plead for help.

“I just want answers,” Ms. Diaz said as she sat in her living room, where a memorial poster from his co-workers at the Paris Las Vegas hotel is still tucked beside the TV. “I want to see them face to face. I want to ask them, was it worth it?”

But so far, nothing.

Detectives in Las Vegas pride themselves on having one of the country’s better track records for solving homicides, clearing nearly eight in every 10 cases while many other big-city departments struggle to solve half of their murders.

But like other big cities across the nation, Las Vegas is in the midst of a dramatic rise in homicides. The rising murder rate is now testing whether the 19 homicide detectives at the Las Vegas Metropolitan Police Department can keep solving those crimes as new calls pour in, from parks awash in heroin, from streets where gang allies are quick to draw their guns, and from poor neighborhoods that lie just blocks from the shimmering casinos of the Strip.