Butler police suspect two men — one armed with a rock — robbed another man of $700 Saturday night in the city.

One suspected robber, Christopher A. Gratzinger, 25, who has no known address, is wanted on an arrest warrant. Police are seeking the other unknown suspect.

The alleged victim, 23-year-old Timothy Claypool of Butler, appeared at the Butler police station about 10:30 p.m. Saturday, reporting he was just robbed, investigators said.

He told police that earlier that night he was at a home with Gratzinger and a black man he only knew by the street name “Memphis.”

While at the home, Claypool said the two men saw him with $700 in currency in his wallet, according to court documents.

Gratzinger and “Memphis” suggested they all go to a convenience store on South Main Street.

Claypool recounted that as they walked on South Jackson Street near West Campbell Street, Gratzinger grabbed him from behind, documents said, and held his hands down.

“Memphis,” he said, had one hand under his sweatshirt and extended out, as if he was holding a gun. He threatened to shoot Claypool.

The two suspects allegedly punched Claypool. He said Gratzinger also choked him.

“At one point Gratzinger was holding a large rock over his head threatening to hit Claypool with it,” according to a police affidavit,

Claypool suffered bumps and bruises, said Butler police Capt. David Dalcamo, but Claypool did not require medical treatment.

The two suspected robbers took the money from his wallet, police said, and took off toward the store.

District Judge Pete Shaffer on Tuesday issued an arrest warrant for Gratzinger on charges of robbery, terroristic threats and receiving stolen property.

Police have no idea of his whereabouts, Dalcamo said. They also have few clues about the other man’s identity.