Why prosecutors call this Arizona man 'very dangerous'

Kyle Collins called 911 claiming he'd come home to find his girlfriend unresponsive. He now faces charges of first-degree murder and kidnapping.

Officials with the Mesa Police Department and local emergency services responded to an apartment complex in downtown Mesa just after 11am on Tuesday, July 21, after a report of a medical emergency, according to ABC 15, Fox 10 and AZ Family.

Girlfriend found dead with significant injuries

Collins, 37, told dispatchers he'd found his girlfriend unresponsive and claimed he had attempted CPR. When police and first responders arrived, they found the woman, later identified as 36-year-old Cierra Tellez, dead in the apartment with significant injuries.

Collins and Tellez lived together and were in a relationship, according to the outlets, which cited police. Following a preliminary investigation, authorities determined there was probable cause to arrest Collins, taking him into custody on Friday, July 24.

Prosecutor calls case 'brutal and horrific'

"This was a very brutal and horrific murder," a prosecutor said during Collins' initial court appearance, according to video shared by AZ Family. "We believe that Mr. Collins is a very dangerous individual."

Collins is currently being held on a bond of $1,250,500, AZ Family and Fox 10 reported.

Neighbor recalls warning signs

A neighbor of the couple told AZ Family he was left "speechless" by Tellez's death. He said he'd played Monopoly with Collins the evening before the alleged murder and noticed nothing unusual.

"Everything was fine, nothing was off," the neighbor, who asked to remain anonymous, recalled.

The following morning — the day of the 911 call — the neighbor said Collins appeared extremely upset and told him he'd gotten into a fight with his girlfriend.

"He came out, flipping out," the neighbor said. "He came and knocked on my door and was telling me about it, and then went and called his mom and was on the phone with his mom for an hour."

Discrepancy over work claim

The neighbor said Collins told him he was heading to work that day. Prosecutors, however, said Collins' boss confirmed he never showed up, according to AZ Family.

The investigation remains ongoing. The Mesa Police Department did not immediately respond to PEOPLE's request for comment, and it's not clear whether Collins has legal representation.