Kenneth Dale Wakefield, a transient, mentally ill Phoenix man, smoked two different drugs before he went on a late July killing spree that resulted in the decapitation and death of his wife and their two dogs.

Wakefield, 43, who is being held on $2 million bond, told police that an hour before the attacks, he smoked marijuana and Spice — a name for synthetic marijuana, a drug that is now feared to be causing violent outbursts in those who may already be mentally ill or are taking psychiatric medicine. Wakefield told police he was trying "to get the evil out" of the victims, according to Reuters. In the process, he also severed his own arm and gouged out one of his eyes, police said.

Wakefield's rampage is one of a string of violent incidents in recent months with a connection to synthetic marijuana. Police say a man who went on a stabbing spree in the Washington, DC Metro on Independence Day is believed to have used the drug, as did two Michigan men before they attacked a family with baseball bats in April. Additionally, a "bad batch" of the drug was blamed for a grisly domestic violence case in Houston in July, when a man stabbed, beat, and fatally choked his girlfriend, police said.

On Monday, New York City Police Commissioner Bill Bratton held a press conference to warn the public and officers of the dangers of synthetic marijuana — which he described as "weaponized" marijuana that gives users super-human strength and immunity to pain. Bratton showed videos of users high on synthetic marijuana at the news conference, showing one man naked on all fours in the middle of the road slapping the ground and yelling, and another naked man breaking through a fence with his body.

"These individuals, many of them under the influence of this drug, are totally crazy," Bratton said.

"It looks like marijuana, but it's lacedwith chemicals and as fast as we are able to identify the chemicals and get that particular chemical, make it against the law, they change the make up of it," Bratton said. "So it's synthetic and it's incredibly dangerous and harmful."

The drug is made by spraying synthetic cannabinoids — chemicals produced in China — on crushed up herbs, then packaging it into bags that sell for about $5 a pop, according to information from the city and Drug Enforcement Administration. The chemicals mimic the active ingredient in marijuana, THC, but create a unique reaction. And the exact combination of chemicals used changes frequently, public health officials say. The DEA has banned multiple synthetic cannabinoids in recent years to try and keep up with the drug's evolution.

Bratton's announcement came almost exactly a year after New York's Health Department first issued a public health warning about Spice after 15 people had adverse reactions to it during a two-day period in July, 2014.

"K2, Spice, Green Giant — no matter what you call it, synthetic cannabinoids are dangerous and illegal," Health Commissioner Dr. Mary Bassett said at the time. "I urge people not to use these products, which have caused a huge spike in emergency room visits this year."

The American Association of Poison Control Centers said that synthetics were first seen in 2009 and grew in popularity around the country after that. According to the National Institute on Drug Abuse, synthetic marijuana has been available for purchase at head shops and gas stations. Bratton said the drug could be purchased at some New York City bodegas. The NYPD announced that last week officers recovered 1,300 bags of synthetic marijuana marketed as K2 from behind a deli counter in East Harlem amid "multi-agency inspections" of the area.

The DEA also reports the drugs can be obtained via the internet from websites based in China. The crushed up herbs often include one called damiana, which is native to Central America, Mexico, and the Caribbean, according to the DEA.

In 2015, poison centers have so far received reports of 5,053 exposures to synthetic marijuana through July 6, with the highest numbers concentrated in New York, Mississippi, and Texas, according to the AAPCC. The drugs, they warn, are made specifically to be abused, "and users don't really know exactly what chemicals they are putting into their bodies."

The NYC Health Department and AAPCC list the reactions to synthetics as agitation, anxiety, fast racing heartbeat, high blood pressure, nausea and vomiting, muscle spasms, seizures, hallucinations, psychotic episodes, and suicidal thoughts and actions, though the Health Department said the effects typically do not last more than one to two hours.

New York University Medical Center researcher Joseph J. Palamar studied usage of synthetic marijuana among teens in 2011 and found that 1 in 10 teens had tried it at least once. Palamar said that for the hundreds of thousands or more who have tried the drug and had no reaction, Bratton's strongly worded warning might fall on deaf ears. Additionally, he said, the popularity of the drug likely peaked a few years ago, and has already begun to decrease among the general population.

"I'm mainly concerned with the NYPD's message and the media, because what they're talking about are rare effects and they're talking about them as if they occur to all users," Palamar. "The media is reporting that if you use synthetic weed you will have superhuman strength and become impervious to pain, which may in fact be a reaction in a small subset of users, but for most, they don't have that."

Palamar said that the prevalence of synthetic marijuana use is so high — he pointed to his study's findings showing 1 in 10 teenagers trying it, as well as a current study he's conducting that has so far found 1 in 5 individuals at New York City night clubs has tried it — that "running around the street naked is an extremely rare occurrence."

"Something we need to keep in mind is a lot of people who are having adverse reactions are from homeless shelters. Not only is this the main population that is using the drug, but they also have a high probability for having pre-existing psychiatric disorders, and may also be on psychiatric medications, and it could be a very dangerous thing for those that decide to use this drug," Palamar said.

He pointed out that most users prefer to use real marijuana, but those that want to avoid arrest or drug detection will often turn to the synthetic alternative, and that "if you are poor and living in a low-resource neighborhood and are already at risk for arrest because of your skin color, you're probably more likely to try this."

A recent report by VICE offered a dark glimpse into the widespread presence of synthetic marijuana at homeless shelters and the effect the drug is having on local hospitals and EMT workers.

Palamar said that instead of the NYPD warning the public that all users can become manically violent, the city and other public health officials should take a more straightforward approach to educating the public.