Ramaj Poller tried to run Monday morning from the Chester police officer who responded to a call complaining that the 18-year-old and his friends were smoking marijuana outside a home in the Delaware County city, according to investigators.

But when the officer lost his footing, authorities say, Poller jumped into a nearby Jeep and tried to run him down, stopping only when the officer fired his gun at the vehicle speeding toward him.

Within 48 hours, police had Poller in custody, and his arrest for attempted murder led to a major break in an unrelated case, a “brutal Christmas Eve murder” in Upper Darby, according to District Attorney Jack Stollsteimer.

“This case represents one of the worst things we could see in Delaware County or anywhere,” Stollsteimer said Thursday in announcing the charges against Poller. “He tried to kill a police officer to escape a murder charge.”

Poller was arraigned Thursday morning, charged with first-, second- and third-degree murder in the death of Samir Geiger, who police say was killed by a group of men looking to rob him of an illegal gun he was carrying.

There was no indication that Poller had hired an attorney. He was denied bail due to the nature of the charges he faces.

His is the third arrest made in the case. Jazmar Thomas, 19, was arrested days after the shooting, and Jamir Hughes, 20, was taken into custody in July, according to court records. Like Poller, they face murder and related charges in the case.

Geiger, 20, was found dead outside a home on Margate Road in Upper Darby on Christmas Eve, according to the affidavit of probable cause for Poller’s arrest. A witness told detectives Geiger was at her home that night and had received a call minutes earlier to meet someone outside.

Hours later, on Christmas, detectives found an Infiniti sedan that matched the description of the vehicle seen fleeing the shooting on fire in Darby Borough, the affidavit said. From the car, which had been reported stolen from a liquor store in Wilmington, detectives recovered fingerprints belonging to Thomas and Poller.

Investigators obtained search warrants for cell phones belonging to Thomas and Hughes, who they discovered had been communicating about stealing cars in Delaware County and Philadelphia, according to the affidavit.

In an interview with county detectives, Hughes admitted that he, Thomas, and Poller had plotted to lure Geiger to a meeting in Upper Darby under the pretext that they would go “rob places” together, the affidavit said. However, the group’s intention was to steal a Glock pistol that Geiger had, because the gun Hughes was carrying “didn’t work.”

After meeting up with Geiger, Poller shot him several times before taking his gun and phone and fleeing in the Infiniti, according to the affidavit. After leaving the scene, the car broke down, the affidavit said, and the three robbers pushed it into a nearby parking space and set it on fire with lighter fluid.