An Oregon man accused of killing his 3-year-old son and the boy's 25-year-old mother was arraigned on murder and kidnapping charges Tuesday and will be held without bail.

Michael John Wolfe, 52, is charged with two counts of aggravated murder, one count of aggravated murder with domestic violence and two counts of kidnapping, according to court documents.

His son, William "Billy" Fretwell, and the mother of the child, Karissa Alyn Fretwell, were reported missing May 17, according to the Salem Police Department. Although investigators have not found any bodies, they say there's probable cause to believe Wolfe killed them.

Karissa Alyn Fretwell and her 3-year-old son William "Billy" Fretwell. Salem Police Department / AP

"Without having the bodies, it makes the case more complicated. But I will say, in sum, the evidence that has been gathered is all leading to a consistent conclusion that they’ve been murdered," Yamhill County District Attorney Brad Berry said, according to NBC affiliate WDSU. Authorities are continuing the search for the mother and son.

Fretwell verified through DNA testing last year that Wolfe was her son's father, and he had recently been ordered to pay $900 a month in child support, according to a probable cause affidavit. A babysitter told police that Wolfe and the woman he's married to had threatened to take custody of the child.

“Based on the interviews of Karissa’s family and friends, I believe the only known person who would benefit from the disappearance or criminal homicide of Karissa and William is Michael," investigators said in the affidavit.

Michael John Wolfe. Salem Police Department / AP

Wolfe told police that he hadn't had recent contact with Fretwell, but investigators believe they were together around May 13, and have evidence that shows text messages were sent between their phones on May 14, the affidavit said.

Surveillance video outside Wolfe's workplace showed him walking into a wooded area and coming back out with a trash bag May 14, the document said.

Wolfe is being held at the Yamhill County Jail.

CORRECTION (May 31, 2019, 1:39 p.m. ET): An earlier version of this article misstated the date on which Karissa Alyn Fretwell and her son were reported missing. It was May 17, not May 13. (The two disappeared on May 13.)