A 19-year-old man confessed Tuesday to shooting and critically wounding Fort Lupton, CO, Sgt. Christopher Pelton, according to a Greeley (CO) Police Department arrest affidavit.

Matthew Cotter is accused of shooting Sgt. Pelton in an impromptu ambush in which Cotter hid behind a fence and fired at Pelton as the officer approached a home around 10:50 p.m. Monday, according to the arrest affidavit, reports the Denver Post .

Pelton was shot in the face and airlifted to a hospital in critical condition, according to the affidavit, which says he underwent two surgeries. He was in stable but critical condition Tuesday, authorities said. He suffered a shattered jaw and lost teeth, according to the affidavit.

Related: Colorado Officer Critically Wounded in Gunfight

Cotter, who was shot by other Fort Lupton police officers and taken into custody, was arrested on suspicion of attempted first-degree murder, assault with a deadly weapon and threatening a police officer with a weapon, all felonies. Cotter waived his right to an attorney during an interview with Greeley police early Tuesday morning and admitted to firing three to four shots at Pelton, according to the affidavit. He described to police how he carefully aimed at Pelton as the officer approached. He told investigators he caught the officer "off guard."

"I shot, he dropped; they shot, I dropped," he said, according to the affidavit.

KKTV reports that according to arrest papers, the incident began when Cotter allegedly showed up at his ex-girlfriend's home. The girl's mother called police at 8:45 p.m. and said Cotter was threatening to harm her daughter, then kill himself.

When police got to the address, they were unable to locate Cotter. About two hours later, police received another call from the girl's father, who said Cotter parked outside the house, turned his vehicle's lights off, and sent a text to his ex that read, 'It's too late.'"

That phone call was quickly followed by a call from the ex-girlfriend, who told police Cotter was armed and at her front door.

Police went to the address at Ponderosa Place a second time. They again couldn't find Cotter, but according to the arrest affidavit, Cotter was watching them from his hiding place behind the fence. That was when he reportedly shot Pelton.