After deliberating about two hours, a Prince George's County Circuit Court jury convicted a 22-year-old man of first-degree murder yesterday in one of a series of slayings that have plagued the Seat Pleasant area during the last three years.

Nathaniel Damian Marr was convicted of the Dec. 2 killing of Arthur Carroll, 22, who was shot three times after he stepped into a cab outside his home in the 300 block of Goldleaf Avenue in Seat Pleasant.

Marr also was convicted of first-degree assault for wounding the cabdriver, Jimmy Abass, and two counts of using a handgun in the commission of a crime of violence.

Marr could be sentenced to life without parole for the murder, plus 65 years for the other counts, when he is sentenced Aug. 26 by Circuit Court Judge Richard H. Sothoron Jr.

Marr's co-defendant, Curtis Windell Alston, also 22, was convicted last week of first-degree murder and other charges in the Carroll slaying. It is one of 21 slayings that have occurred in the Seat Pleasant area during the last three years that police have attributed to loosely knit gangs engaged in retaliatory attacks.

In February, police announced that they had curtailed the gang activity by arresting seven suspects in eight slayings. Marr and Alston were the first of those defendants to go on trial.

"The police officers worked hard at solving a number of these Seat Pleasant murders. The citizens should be pleased that they invested as much time and did such a thorough job in solving these cases," said Assistant State's Attorney Darlene Soltys, who prosecuted Marr and Alston.

Marr's attorney, Assistant Public Defender Gary Ward, did not return a phone call seeking comment.

In her closing argument, Soltys told the jury that Marr attacked Carroll to avenge the Nov. 29 murder of his cousin, Ronald Anthony "Cheese" Muse, 21. Carroll and two other men robbed Muse, and Carroll shot Muse, according to trial testimony.

Key evidence against Marr included the defendant's statements to police after he was arrested Dec. 30 on a warrant for a separate, nonfatal shooting.

County homicide detectives testified that Marr waived his right to an attorney and gave two similar statements admitting to the shooting.

In an oral statement, Marr said he and Alston went to Carroll's home to confront him about the Muse slaying. Marr said that when he saw Carroll getting into the cab,

"I knew I had to do something" and fired at Carroll, Sgt. Joseph McCann testified.

Later, in a written statement, Marr wrote that he fired at Carroll when Carroll reached for his waistband. Marr wrote that he was afraid Carroll was reaching for a gun, McCann testified.

In her closing argument, Soltys urged jurors to disregard the "self-serving" self-defense claim and convict Marr of first-degree premeditated murder.