(NewsNation) ⁠— The recent killings of four Muslim men in Albuquerque sent a wave of fear through the New Mexico city and prompted some outlets to reference the homicides as the work of a serial killer.

Albuquerque Police Chief Harold Medina said it was not clear yet whether the deaths of four men should be classified as hate crimes or serial killings or both.

On Tuesday, police arrested 51-year-old Muhammad Syed in connection with the deaths of Aftab Hussein, 41, and Muhammad Afzaal Hussain, 27.

Syed has denied any connection to the killings and told authorities he was so unnerved by the violence he was exploring moving his family to Houston.

What we know so far

The first known victim, Mohammad Ahmadi, 62, a native of Afghanistan, was killed on Nov. 7, 2021, while smoking a cigarette outside a grocery store and café that he ran with his brother in the southeastern part of the city.

Syed, however, is charged with murder in connection with two of the four homicides: those of Aftab Hussein on July 26 and Muhammed Afzaal Hussain on Aug. 1, public records show.

Police have said Syed may also be connected to Ahmadi’s death and that of 25-year-old Naeem Hussain.

Each of the men attended the same mosque.

“The offender knew the victims to some extent, and an interpersonal conflict may have led to the shootings,” police said in an official statement.

Investigators are still working to identify how the men crossed paths.

What is serial murder?

The definition of serial murder has changed over time and researchers have debated whether factors such as motive or various kinds of “cooling-off periods” should be taken into consideration.

Former FBI profiler Mary Ellen O’Toole told the Associated Press the description of the crimes of which Syed is accused would fit the definition of a serial killer if he is the perpetrator, adding serial killers often have red flags leading up to homicide.

The generally accepted definition of serial murder and the one cited by the FBI was determined at an International Serial Murder Symposium hosted by the FBI’s Behavioral Analysis Unit in 2005. It considers serial murders unlawful killings of two or more victims by the same offender(s), in separate events. 

Author and forensic psychology professor Katherine Ramsland noted a caveat in her book “Spree Killers” ⁠— co-authored with FBI BAU member Mark Safarik.

Under a strict definition, she wrote, people in gangs, drug cartels, and organized crime syndicates might also meet the criteria by definition, although those kinds of cases aren’t usually included in serial murder research.

Notably, the word “murder” refers to the criminal act of killing another human with malice, meaning an accused person can only accurately be described as a murderer once a conviction has taken place.

Does the designation matter?

The definition created at the 2005 symposium was crafted with researchers and law enforcement in mind.

Researchers, for example, wanted the definition to cite a specific number of requisite murders, which would create more solid criteria for research on serial killers.

A lower number, however, granted law enforcement more flexibility in committing resources to a potential serial murder investigation, according to a 2008 report.

Tracy Walder, a former CIA officer and FBI special agent told NewsNation during an interview Monday that the designation might have made a difference in terms of local versus federal resources that were available while a manhunt was underway.

Since Syed’s arrest on Tuesday, however, community members are focused on their own sense of security as they grieve the deaths of their neighbors.

“We can now come out of fear,” Muhammad Imtiaz Hussain, brother of Muhammad Azfaal Hussain, said Tuesday. “Now we can sometimes leave our door open. Now I can sit on the balcony and drink coffee. Now I can go outside for shopping. Now I can go outside for a walk. Now I can take my kids to the playground.”