PELHAM — With help from an unidentified bystander, police arrested a Manchester man after he fled in a stolen car and crashed into a tree across the town line in Windham yesterday, police said.

The bystander, who pulled over when he saw the crash, helped police arrest Lucas O'Sullivan, 25, of Manchester on charges of disobeying a police officer, possession of a stolen car, driving after suspension and reckless operation of a motor vehicle.

During the arrest, police realized O'Sullivan fit the description of a man involved in a hit-and-run crash Feb. 26 when the driver of a stolen car struck a utility pole near Chunky's Cinema on Bridge Street and fled.

Yesterday, O'Sullivan tried to run after he crashed into a tree off Lowell Road in Windham. He struggled with police, Lt. Brian McCarthy said.

Police ordered him to stop and lie face down, but he refused and tried to get away by climbing over a snowbank, McCarthy said. That's when the unidentified man stepped in and helped police subdue O'Sullivan so they could handcuff him.

Police are looking for the man so they can thank him for his effort, McCarthy said.

After his arrest, O'Sullivan was taken to Parkland Medical Center in Derry, where he was treated for minor injuries suffered in the crash.

The pursuit began yesterday about 9:30 a.m., when Pelham Officer Matthew Keenliside attempted to stop O'Sullivan for speeding on Dutton Road. O'Sullivan fled in a 2002 Dodge Stratus, which was stolen in Manchester, and Keenliside pursued him through Pelham's town center.

O'Sullivan crashed on Lowell Road in Windham, McCarthy said, and then tried to flee on foot.

O'Sullivan was scheduled to be arraigned in Salem District Court this morning.

Police are asking anyone with information about the identity of the man who helped Keenliside and Detective Jim Johnson with the arrest to contact McCarthy at 635-2411.

"He risked his safety to assist the officers," McCarthy said, "and we would like to thank him." An investigation of the incident continues with help from the Windham Police Department and state police.

O'Sullivan was being held last night in lieu of $25,000 cash bail. He also faces charges of receiving stolen property — motor vehicle (a felony) and conduct after an accident — leaving the scene (a misdemeanor) in connection with the Feb. 26 crash. The car was stolen in Manchester, police said.