St. Paul police have arrested three adults and a teenager in an armed robbery turned sexual assault early Tuesday that authorities are calling an “unconscionable” crime.

Officers were sent to a parking lot near Raspberry Island at 2 a.m. on a report of a robbery and sexual assault.

There, police found two boys ages 15 and 16, and two 18-year-old women who said they were in a parking lot nearby when they were approached by four men. One brandished a gun and demanded that they get on the ground and hand over their valuables.

After the four complied, the women were forced into a nearby vehicle and were sexually assaulted by at least one of the suspects. The four suspects then fled on foot.

Police said witnesses “provided crucial information that allowed the investigation to move forward quickly.

Officers shared the information with nearby agencies, and a short time later West St. Paul police arrested three suspects in an unrelated robbery who matched the descriptions of those in the Raspberry Island incident. Investigators identified a fourth suspect arrested Tuesday. The suspects are ages 20, 19, 18 and 16. The Star Tribune generally does not name suspects until they are charged.