CHANDLER, Ariz. (AP) — The gruesome case of a man who was stabbed and beheaded in a suburban Phoenix apartment has police investigating whether the killing is potentially the most extreme example of Mexican drug cartel violence spilling over the border.

Martin Alejandro Cota-Monroy’s body was found Oct. 10 in a Chandler apartment — his severed head a couple feet away. One man suspected in the killing has been arrested, and a manhunt is under way for three others.

Detectives are focused on whether the men belong to a Mexican drug cartel, and they suspect that Cota-Monroy’s killing was punishment for stealing drugs. The brutal nature of the killing could be designed to send a message to others within the cartel.

“If it does turn out to be a drug cartel out of Mexico, typically that’s a message being sent,” said Chandler police Detective David Ramer. “This person was chosen to be executed. It sends a message to other people: If you cross us, this is what happens.”

Decapitations are a regular part of the drug war in Mexico as cartels fight over territory. Headless bodies have been hanged from bridges by their feet, severed heads have been sent to victims’ family members and government officials, and bags of up to 12 heads have been dropped off in high-profile locations.

More than 28,000 people have been killed in Mexico in drug-related violence since December 2006, when President Felipe Calderon deployed soldiers to battle the cartels in their strongholds.

If the suspects in the Arizona case belong to a cartel, the crime could be the only known beheading in the U.S. carried out by a drug cartel, said Tony Payan, a political science professor at the University of Texas at El Paso who has done extensive research about border violence.

The killing could also affect the immigration debate in Arizona. Supporters of the state’s controversial immigration law frequently cite this type of violence as reason to crack down on illegal immigrants. The decapitation victim and the suspects were all illegal immigrants.

Republican Gov. Jan Brewer drew criticism this year for claiming that headless bodies were being found in the Arizona desert as she sought to bolster her argument for immigration reform. She later backtracked on those claims, but said such violence in the broader border region is cause enough for alarm.

The killing has unnerved residents in the neighborhood and apartment complex where Cota-Monroy was killed.

The tiny, run-down complex sits along a side street across from ramshackle trailer homes in a neighborhood not far from brand-new strip malls with big-box stores in the suburb of Chandler.

No one is living inside the apartment that is the scene of the crime. There’s beat-up leather furniture, a bouquet of flowers and a candle on a dining-room table, and the kitchen cabinets are ajar, as if someone left in a hurry.

“I’m terrified,” said Norma Alvarado, a 47-year-old housekeeper who lives two doors down from the apartment. “I’ve lived here for 20 years and I’ve never heard of that (decapitation) happening, and it was so close to us. … Maybe they’re copying what’s happening in Mexico.”

Alvarado, who lives alone with her three children, said she’s moving the family away from the complex out of fear that those responsible will return to the area looking for revenge.

The victim and three of the suspects had traveled to Chandler from where they were living in Perris, Calif., and were staying at a hotel. They met the two men who live in the apartment at a bar the night of the killing, and the group returned to the apartment.

The killing occurred around 5 a.m. after the men living there were out of sight, one sleeping in a bedroom and the other outside talking to his girlfriend. They stumbled upon Cota-Monroy’s decapitated body and called police.

Three of the suspects had fled, but police say a fourth suspect who lived in the apartment complex went home. Crisantos Moroyoqui, 36, was found sleeping inside wearing pants covered in blood.

Shortly before the killing, Moroyoqui was heard asking Cota-Monroy: “Who are you? Who are you?” in an aggressive tone, according to a police report.

Moroyoqui was arrested and charged with second-degree murder and hindering prosecution. He pleaded not guilty on Wednesday and has refused to speak to police. He declined to speak with The Associated Press.

The other suspects have been identified as Jose David Castro Reyes, 25; Isai Aguilar Morales, 22, and a man between the ages of 20 and 27 only known by the nickname “El Joto,” a derogatory Spanish term for a gay man.

They are believed to have fled to Mexico, making it very difficult to locate them.

While extreme violence has stayed south of the border for the most part, some of it has spilled over into the U.S.

In March, Arizona rancher Robert Krentz was gunned down while checking water lines on his property near the border. Authorities believe — but have never produced substantive proof — that an illegal immigrant, likely a scout for drug smugglers, was to blame for his killing.

In May 2009, a Mexican drug cartel lieutenant who became an informant for U.S. Immigration and Customs Enforcement was shot eight times outside his pricey home in El Paso. The lieutenant, Jose Daniel Gonzalez Galeana, was living in Texas on a visa that ICE gave him, and is believed to be the first ranking cartel member killed in the U.S.

Payan described the spillover as minimal, but said it could increase.

“The cartels warring in Mexico have operatives in Phoenix, and it is possible they may go after each other in places like that,” he said, but added that cartels are very unlikely to target the general American population. “Our law enforcement agencies and intelligence agencies have shown a high degree of competence. In Mexico, they’re nowhere near that level.”

(This version CORRECTS to Perris, Calif., instead of Paris, in 15th paragraph.)