BOULDER, Colo. — The suspect accused of attacking people with a knife on Boulder's Pearl Street Thursday morning told police that voices in his head told him "to go kill people," according to an arrest affidavit Denver7 obtained Friday. He also said he had not taken medication for a serious mental health condition.
Marcus Ariel Valles, 35, of Lakewood faces charges of attempted first-degree murder, felony menacing and first-degree assault, also a felony. The department said additional charges are likely.
▶️ WATCH: Denver7’s Claire Lavezzorio reports on how technology helped track down the suspect in a matter of seconds on Thursday morning.
A police spokesperson told Denver7 on Thursday that a mobile camera unit at 13th Street and Pearl Street allowed officers to get eyes on the suspect within seconds of the initial 911 call. The camera had been placed there after the fatal Boulder firebombing attack in June 2025.
According to Valles' arrest affidavit, that helped first responders quickly identify what the suspect looked like as officers rushed to the scene.
Once Valles was in handcuffs, one of the officers approached a woman who was sitting nearby and appeared in shock. She told officers she had been attacked by the suspect.
"Looking at (her), I quickly observed her left hand, which appeared bloody, likely from a 3-4 inches long laceration which stretched across her hand," a police officer wrote in the affidavit.
Surveillance footage would later show Valles charging at her and attempting to slash and stab at the woman while she tried to protect herself, the document continued.
The officer began First Aid to help the woman before EMTs arrived. As the officer walked away to let the EMTs work, a man approached him and said the suspect had also attacked him. He said the suspect only left him alone after he threw his cup of coffee on him.
A witness, who was in his truck at the time, told police that he had seen Valles attack the woman. He reported that Valles was holding the knife close to his body "in a concealed manner" while walking quickly toward the woman, who was backing away and screaming for him to get away from her, the affidavit said. The witness said they didn't hear or see the suspect say anything. The witness said he yelled for the woman to run to his truck, which she did. She stayed in the backseat until officers arrived.
While the suspect was handcuffed on the ground, he told police "the voices in my head told me to go kill people," the affidavit reads. He made similar statements during the investigation, the document says. He also told police that he had been diagnosed with schizophrenia and was supposed to take medication, but had not done so for the last three months.
"My intentions was to kill somebody," Valles said, according to the affidavit. "I don't know anybody so it is what it is."
He told police that it was better to hurt somebody he did not know that somebody he did know. Police learned he had been living with his girlfriend in Lakewood and they worked to contact her to make sure she was safe. The affidavit does not confirm if they were able to speak with her.
Valles consented to a blood draw and buccal swabs at the Boulder Police Department. Officers noted that during Valles' interview with police, he would smirk and laugh when police left the room, the affidavit reads. He asked multiple times if the woman he had attacked was OK.
The affidavit reads that police recommended three counts of attempted first-degree murder because in addition to the two attacks listed above, he had also followed a woman at a distance with the knife in his hand.
The woman who was injured in this case had her lacerations closed at a local hospital, "as they had been deep in nature," the affidavit reads.
Anyone with any information about the suspect or this crime is asked to contact detectives via the Boulder police tipline at 303-441-1974 and reference case 26-05470.
Call or text 988 to contact the Colorado Mental Health Line, which is available 24/7. The Colorado Disaster Distress Helpline is available via call or text at 1-800-985-5990. Find more mental health resources in Boulder and beyond here.
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