Benton County Sheriffs officials say the person was picked up on an unrelated charge, but is being detained.

Early Tuesday afternoon, officials said the three murdered people had crossed over to Washington from Umatilla, OR, and their time of death was around 4 a.m. Saturday. Their bodies were discovered later that morning by a farm worker near Coffin Road in a rural area.

The Benton County Coroner also released information on the cause of death. 19-year-old Victoria A. Torres was shot in the neck, and the bullet hit major arteries and her spine.   23-year-old Abigail Torres-Renteria (no relation to Victoria) was also shot in the neck, the bullet hitting her brain stem.  She was pregnant with what Coroner John Hansen's report said was a "near full-term female baby" who didn't survive.

22-year-old David Saucedo was shot twice in the head, causing "non-survivable injuries" to his brain.

Dr. Selove, a forensic pathologist from Seattle, conducted the autopsies, according to the report.

Authorities didn't say which jail the person of interest is being detained at.