GOLDEN, Colo. -- Joseph Trujillo put his 5-month-old son on a bed, wedged by pillows with a bottle of formula on his chest, then went out for about 7 hours of playing "beer pong" and drinking shots at a bar and house party, according to court records.

The 23-year-old father told investigators he finally returned home about midnight on Jan. 20 to find his baby boy's lifeless body on his back on the bed where he left him, according to an investigator's statement supporting Trujillo's arrest.

Read Joseph Trujillo's Arrest Affidavit

While Jefferson County sheriff's investigators initially recommended a first-degree murder charge against Trujillo, prosecutors formally charged him with felony child abuse resulting in death. He remains in jail with his bond set at $50,000.

The coroner has not ruled on what caused the infant's death, pending additional tests.

Investigators say Trujillo was initially adamant that he'd only left home for "20 minutes" to " get a quick drink" with a woman friend. But the woman told authorities Trujillo, whom she'd met on Facebook, was out for at least 7 hours, the arrest affidavit stated.

Trujillo's mother, Gay Lujan, who lives with him at the West 10th Avenue apartment, told investigators she returned from work about 10:15 p.m. and found music blaring in her son's room and the baby's crib empty.

"She believed Joseph was at the bar because he has a drinking problem," the grandmother told investigators, according to the affidavit. "She was concerned he took Adrian with him to the bar."

"She sent him a few text messages stating, 'Get the baby home' and 'Where are you?'" the arrest report stated. But her son didn't respond.

The grandmother said she was awakened about 12:30 a.m. by the sound of Joseph crying on the phone to someone.

"She got up and saw Adrian lying on the couch. She touched him and felt he was stiff and cold," the affidavit stated. The woman called 911.

An arriving paramedic found the baby cold and pale with his arms raised up around his head. The paramedic noticed a one inch-wide discoloration on the dead infant's temple, the arrest affidavit said.

The young father was kneeling on the kitchen floor, crying and "mumbling incoherently," the arrest affidavit stated.

Trujillo changed his story a couple of times as investigators confronted him with the woman friend's and his brother's accounts that he had been out at the Rock Rest Bar, playing pool, drinking beer and shots of tequila, the affidavit stated.

Jonathan Trujillo, 25, told investigators his brother said their cousin "Shelly" was babysitting Adrian, the affidavit stated.

The woman friend recounted how they'd left the bar to go to an apartment across the street and "played beer pong" for about an hour, the arrest affidavit stated. Beer pong is a drinking game where players toss a ping-pong ball into a beer glass to force an opponent to chug.

The couple then drove to Taco Bell for a meal before driving home and sitting in the car parked outside Trujillo's apartment until about 11:30 p.m., when the woman told investigators she went home.

After entering the apartment alone, Trujillo said he found his son was still on the bed on his back, but he "he was purple and blue with his hands up by his head," the affidavit stated. "He was cold and wouldn't move."

The father said he "freaked out" and called his woman friend," the affidavit stated. The woman told authorities: "He was hysterical and sobbing. He repeated several times that his son was dead."