Ryker was pronounced dead at a Salt Lake City hospital. Petersen, 21, was booked into the Utah County jail on suspicion of aggravated murder, a first-degree felony.
On Monday, American Fork police Sgt. Gregg Ludlow described Ryker's death to Judge David Mortensen, which Johnson said was necessary in order to ask for the no-bail hold.
"Mr. Petersen advised that he had been planning to kill the child for about a month," Ludlow said Monday. "And decided that Friday was the day that he was going to do that."
Ludlow, who became emotional as he read the details of the case, said Petersen told police he took the child into the basement of his home and placed him on a couch. He went into another room, loaded a single round into a .22 caliber rifle, went back into the room and shot the infant in the forehead, Ludlow said.
Police said a relative stopped the man before he turned the gun on himself.
"He stated that his intention was to kill himself after that," Ludlow said during Monday's hearing.
Petersen, who appeared in court via a video feed Monday morning, appeared emotionless while the details of the case were read in court. Mortensen advised the man not to speak about the case during the hearing, since he did not yet have an attorney.
Petersen has no criminal history, according to a search of Utah court records. Depending on the severity of the homicide charge filed against him and aggravating factors, Petersen could face anything from life in prison to the death penalty.
A Paypal account has also been set up to help the family give Ryker "an amazing funeral," according to a Facebook page about a vigil that was held Sunday. Donations at Paypal are to be sent to firstname.lastname@example.org with "Baby Ryker" in the subject line.