Bismarck police said they foiled a couple's plans to rob a local gas station Wednesday night by jailing them before they could try.

Randy Prettyman and Sally Weiss had black clothes, leather gloves and ski masks in their car when police stopped them at 7:45 p.m. in the 2100 block of East Divide Avenue, Bismarck Police Lt. Dan Donlin said. Authorities had information that the couple planned to rob Gas Plus, 1309 E. Interstate Ave., when it closed later that night.

Prettyman, 21, and Weiss, 22, were picked up after they took a "substantial step towards their plan," Donlin said, but declined to comment further on what that step was. Police had been watching the couple since Monday when they received a tip about the robbery plans.

Burleigh County Assistant State's Attorney Cynthia Feland said Prettyman and Weiss also conducted surveillance of the gas station and mapped out their escape route.

"There was a multitude of things they did, not just one overt act," Feland said. "It was a fairly well thought out plan."

Investigators found a wooden rod in the couple's car that Feland said they intended to use in a "strong-armed style" robbery. There was no indication that Prettyman or Weiss was planning to use a gun in the heist, Donlin said.

"But for this individual coming in, we'd be looking at investigating an actual robbery rather than a conspiracy to commit one," Feland said.

Prettyman and Weiss were charged Thursday with conspiracy to commit strong-armed robbery. The class A felony includes a maximum sentence of 20 years' imprisonment and a mandatory minimum of four years. They're being held in the Burleigh County jail on $10,000 cash bonds.

(Reach reporter Mike Albrecht at 250-8261 or cops@ndonline.com.)