Authorities have heightened their alert in South Dakota as they intensify the search for the individual responsible for fatally shooting a Minnesota lawmaker and her husband, while also injuring another lawmaker and his spouse early on Saturday.

On Sunday, Sen. Amy Klobuchar, D-Minn., mentioned on NBC’s “Meet the Press” that although there is a possibility that the suspect, 57-year-old Vance Luther Boelter, may still be in Minnesota, authorities are urging South Dakota residents to remain vigilant.

“They’ve also put an alert out in South Dakota,” Klobuchar said, adding that the suspect is still believed to be in the Midwest.

Boelter is charged with the murder of former Minnesota House Speaker Melissa Hortman and her spouse, Mark, in their home in Brooklyn Park early Saturday. State Sen. John Hoffman, also a Democrat, and his wife, Yvette, sustained injuries from gunfire at their Champlin residence located about nine miles away.

Authorities have said the lawmakers were targeted.

The FBI shared images of Boelter appearing to impersonate a police officer and wearing a mask while on the doorstep of one of the lawmaker’s homes. A second photo shows him wearing a tan cowboy hat at a Minneapolis business shortly after the shootings.

The FBI named Boelter to its most wanted list and is offering a $50,000 reward for information that leads to Boelter’s arrest and conviction.

Fox News’ Danielle Wallace, Michael Dorgan and Julia Bonavita contributed to this report.