A University police detective arrested two men at gunpoint near the Harvard Medical School after chasing their green Chrysler LeBaron through the Roxbury section of Boston last week, police said.

The officer, Detective Richard Mederos, was working an overtime patrol on September 6 around 1:00 p.m. when he heard shots being fired and saw the car back out of an alley on Parker St.

The LeBaron then began to chase a red van, when one of the men leaned out of the passenger-side window and fired four to six shots at the van, police said.

The alleged assailant, Miquel Pena, 26, of Dorchester, wounded the driver of the red van, which then sped away onto route 93. The van's driver eventually flagged down a state trooper to get medical assistance, according to police.

But Mederos followed the green car, which he pursued through several of Roxbury's narrow back streets. Three of the men in the car bailed out near the Bromley Health housing project, according to Lt. John F. Rooney.

Mederos then stopped two of the men at gun-point, while two Bromley Health security officers stopped the third.

In addition to Pena, the two other men arrested were Renaldo Velle, 21, of Dorchester and Jose Perez Rodiquez, 35, of Roxbury, police said. The fourth man in the car is still at large.

All three of the men arrested were charged with assault with intent to murder, assault with a dangerous weapon, unlawful possession of a firearm and discharging a firearm within 500 feet of a building, Rooney said.

Pena, Velle and Rodiquez will be arraigned in Roxbury District Court on October 6, police said.