A 29-year-old man killed his girlfriend's 7-month-old son in her central Minnesota home with punches to the head while the boy's 4-year-old brother watched, according to charges filed Thursday.

James J.R. Wood, of St. Joseph, Minn., was charged Thursday with second- and third-degree murder and first-degree murder in connection with the death Saturday morning of Noah Belgarde in a home in Watab Township, southeast of Rice in Benton County.

A medical examiner's autopsy found Noah suffered several deadly skull fractures and bruising.

Wood left the home later Saturday morning and was arrested about 5:20 a.m. near Royalton on drunken-driving and assault charges. While in custody in the Morrison County jail, he refused a preliminary breath test, physically resisted being led into his cell and punched a sheriff's deputy, the criminal complaint read.

Wood appeared in court Thursday and remains jailed in lieu of $500,000 bail. A message was left with his attorney for comment about the allegations.

Noah "was an active little boy and full of love," read his online obituary. "Squash and sweet potatoes were his favorite foods, and he loved bath time.

"He was the best little brother."

According to the murder charges:

Kateri Belgarde called 911 about 10:20 a.m. Saturday and said her little boy was dead. Emergency responders located Noah, cold to the touch and bruised on his face and head.

Belgarde said that Wood, as he had been doing for the past month or two, arrived Friday about 7:30 p.m. intending to stay until Monday morning.

Noah was put down for the night about 8 p.m. After her 4-year-old boy went to sleep, Belgarde joined Wood in the attached garage for drinks before she went to bed between 11:30 p.m. and midnight. Wood stayed up.

When Belgarde awoke at 10 a.m. Saturday, she noticed that Wood and his vehicle were gone. She texted him in vain.

A deputy who was dispatched after the 911 call heard Belgarde ask her 4-year-old whether he saw anything. "Oh, James hit him," the boy said.

In a later interview with investigators, the boy described Wood as being "naughty" and demonstrated what he saw by hitting himself on his forehead and saying, "Like that."